Dr Ayson said the US had 37,000 troops in South Korea and casualties would be high. Pyongyang had an estimated 80,000 artillery pieces concentrated on the area and may use non-conventional chemical weapons.

Despite the risks, Dr Ayson, a specialist in North Asian strategy, said the US military option was a real possibility, given Mr Bush has said he could not tolerate a nuclear North Korea.

"Military action is now more likely after the test, but is probably less than 50 per cent (likely)," Dr Ayson said.

US intelligence sources said the Bush Administration was considering naval action around North Korea, stopping short of a blockade but intercepting and inspecting all ships off the peninsula.

Analysts estimate North Korea may have enough nuclear material for a dozen weapons and has built two or three, but is yet to miniaturise them enough for long-range missiles.

The major threat its nuclear capacity posed was the potential for it to sell a bomb to a terrorist group that would sail it to a US port, or the possibility for it to drop a device from an aircraft over a major city.

The regime has claimed to have had nuclear arms since 1995; they are mainly plutonium-based but North Korea is also known to be developing uranium-based material.

Dr Huisken said China would be angered by North Korea ignoring its demands in recent weeks not to conduct the test -- a factor that should lead to quick agreement by the UN Security Council for economic and diplomatic sanctions against the regime.

"For the first time in four years Seoul, Beijing, Tokyo and Washington would be prepared to agree that this is an intolerable development," Dr Huisken said.

"I think the hardest part will be to agree on how far to go."

But US military strikes could eventuate if the UN process gets bogged down, military analyst Derek Woolner said.

"Military action is possible but it is more important to get a strong international diplomatic response," he said.

China, North Korea's main ally and benefactor, would now increase its pressure on Pyongyang, including the possibility of withdrawing financial and food support, which could leave millions more North Koreans at risk of starvation.

Mr Woolner said the nuclear crisis might also drive the US and China closer together.

Iran, which continues to ignore international pleas to abandon its nuclear program, is also likely to be encouraged if North Korea is not dealt with harshly.

Mr Woolner said the US and Australia had been concerned for some time about North Korea's desire to spread missile technology and the potential for it to share its nuclear developments with Iran and others.

Mr Woolner said the US would redouble its efforts to destabilise Kim Jong-il from within North Korea, but its isolation made that prospect difficult and he faced no established opposition.

"There are continuing whispers about just how strong his grasp on power is," Mr Woolner said.

But others, including Dr Ayson, believe the military leadership in Pyongyang fully supports North Korea's entry into the nuclear arms club.

North Korea has close defense ties with Iran and Syria and has been a major source for the supply of surface-to-surface missiles and ballistic missile knowhow to both countries.

The senior Israeli official also warned that the North Korean nuclear test is likely to result in Tehran expediting its nuclear development program, because of the assumption that a state with nuclear arms is "immune" to a strike against its nuclear installations.

"Now that North Korea has proven nuclear capabilities, it is liable to collaborate with Iran and accelerate the Iranian nuclear program," Israel's ambassador to the United States Danny Ayalon said.

An Iranian diplomat involved in talks with the European Union on his country's nuclear ambitions said Monday that the North Korean test is likely to make the West think twice about its attitude toward the Iranian nuclear program.

The diplomat also voiced a veiled threat that Tehran would one day go the way of Pyongyang.

The North Korean test comes at a time when the United States is making efforts to rally international support for sanctions against Iran because of its disregard for a UN Security Council demand that Tehran freeze its uranium enrichment program.

However, senior European and American diplomatic sources opposed any comparison between the deadlock on Iran's nuclear program and North Korea, saying that these were different problems requiring different solutions.

The Israel Atomic Energy Committee confirmed Monday that North Korea had carried out a nuclear test, on the basis of seismologic data. According to the press release, the subterranean explosion was relatively small, with an estimated yield of 0.5 and 1.0 kiloton.

Israel joined the chorus of nations throughout the world Monday who condemned the North Korean nuclear test and also called for a continuation of the "moratorium on nuclear tests." The international community must "firmly implement UNSC resolutions adopted to deal with weapons of mass destruction and the proliferation threat," a statement read.

Tehran was reserved in its reaction to the North Korean test, and did not condemn Pyongyang. "Any step that threatens global peace and security is not acceptable to Iran," a senior official said.

Iran's state radio was more blatant and blamed Washington for the North Korean test.

"The U.S. not only failed to remove the sanctions it imposed on North Korea, but even stepped up diplomatic pressure against it. In the end, such pressure resulted in North Korea holding a nuclear test. The nuclear test of North Korea is a response to American threats and humiliations."

European and other intelligence sources claim that North Korean scientists offer assistance to Iran in the development of its nuclear program.

North Korea helped Iran develop its Shehab-class of surface-to-surface missiles.

"I suspect (Vice-President Dick) Cheney and (Defence Secretary Donald) Rumsfeld might argue we now know (they've got the bomb) and we've got to do this some time.

"I think they have an eye also on Iran. You certainly can't rule (an attack) out."

The ANU centre's director, Robert Ayson, said the stakes were high.

He said the problem the US faced in attacking would be North Korean leader Kim Jong-il's promise to turn South Korean capital Seoul into "a sea of fire" and the potential for it to launch missiles on Japan.

Dr Ayson said the US had 37,000 troops in South Korea and casualties would be high. Pyongyang had an estimated 80,000 artillery pieces concentrated on the area and may use non-conventional chemical weapons.

Despite the risks, Dr Ayson, a specialist in North Asian strategy, said the US military option was a real possibility, given Mr Bush has said he could not tolerate a nuclear North Korea.

"Military action is now more likely after the test, but is probably less than 50 per cent (likely)," Dr Ayson said.

US intelligence sources said the Bush Administration was considering naval action around North Korea, stopping short of a blockade but intercepting and inspecting all ships off the peninsula.

Analysts estimate North Korea may have enough nuclear material for a dozen weapons and has built two or three, but is yet to miniaturise them enough for long-range missiles.

The major threat its nuclear capacity posed was the potential for it to sell a bomb to a terrorist group that would sail it to a US port, or the possibility for it to drop a device from an aircraft over a major city.

The regime has claimed to have had nuclear arms since 1995; they are mainly plutonium-based but North Korea is also known to be developing uranium-based material.

Dr Huisken said China would be angered by North Korea ignoring its demands in recent weeks not to conduct the test -- a factor that should lead to quick agreement by the UN Security Council for economic and diplomatic sanctions against the regime.

"For the first time in four years Seoul, Beijing, Tokyo and Washington would be prepared to agree that this is an intolerable development," Dr Huisken said.

"I think the hardest part will be to agree on how far to go."

But US military strikes could eventuate if the UN process gets bogged down, military analyst Derek Woolner said.

"Military action is possible but it is more important to get a strong international diplomatic response," he said.

China, North Korea's main ally and benefactor, would now increase its pressure on Pyongyang, including the possibility of withdrawing financial and food support, which could leave millions more North Koreans at risk of starvation.

Mr Woolner said the nuclear crisis might also drive the US and China closer together.

Iran, which continues to ignore international pleas to abandon its nuclear program, is also likely to be encouraged if North Korea is not dealt with harshly.

Mr Woolner said the US and Australia had been concerned for some time about North Korea's desire to spread missile technology and the potential for it to share its nuclear developments with Iran and others.

Mr Woolner said the US would redouble its efforts to destabilise Kim Jong-il from within North Korea, but its isolation made that prospect difficult and he faced no established opposition.

"There are continuing whispers about just how strong his grasp on power is," Mr Woolner said.

But others, including Dr Ayson, believe the military leadership in Pyongyang fully supports North Korea's entry into the nuclear arms club.

U.S. President George W. Bush called the test provocative, "unacceptable" and a threat to global peace and security. He said the action deserves "an immediate response by the Security Council.

"The transfer of nuclear weapons or material by North Korea to states or non-state entities would be considered a grave threat to the United States," Bush said. "And we would hold North Korea fully accountable for the consequences of such action."

Pak Gil Yon, North Korea's UN ambassador, said the Security Council should congratulate his country instead of passing "useless" resolutions or statements.

According to the Associated Press, the draft resolution proposed a trade ban on military and luxury items, the power to inspect all cargo entering or leaving the country, and freezing assets connected with its weapons programs.

'Dangerous act': Harper

Canadian Prime Minister Stephen Harper called the test an "irresponsible and dangerous act" that seriously undermines both regional peace and stability, and global efforts to halt the spread of nuclear weapons.

He said Canada believes that North Korea's security, economic and political goals are best achieved through the framework of the existing six-party talks to address the North Korean nuclear crisis.

Bush said U.S. officials were still trying to confirm that a nuclear explosion had taken place.

Still, he said, "such a claim itself constitutes a threat to international peace and security. The United States condemns this provocative act."

Japanese Prime Minister Shinzo Abe, in Seoul for a summit with South Korean President Roh Moo-hyun, called for "harsh measures" against Pyongyang and warned of the dawn of a "dangerous nuclear age."

"The development and possession of nuclear weapons by North Korea will in a major way transform the security environment in North Asia and we will be entering a new, dangerous nuclear age," he said.

According to North Korea's official news agency, the reclusive country tested its first nuclear weapon on Sunday.

No radiation reported

The Korean Central News Agency reported that the test was successful and no radiation had leaked from the underground site.

The test "will contribute to defending the peace and stability on the Korean Peninsula and in the area around it," KCNA reported.

The U.S. Geological Survey said it recorded a magnitude-4.2 seismic event in northeastern North Korea. Asian neighbours also said they registered a seismic event, but only Russia said its monitoring services had detected a nuclear explosion.

"It is 100-per-cent [certain] that it was an underground nuclear explosion," said Lt.-Gen. Vladimir Verkhovtsev, head of a Defence Ministry department, according to Russia's ITAR-Tass news agency.

The test took place at 10:36 a.m. local time Sunday (9:36 p.m. ET) near the city of Kilju, according to South Korean defence sources cited by South Korea's Yonhap news agency.

South Korean military on high alert

South Korea, which shares the world's most heavily armed border with the North, said it put its military on high alert.

North Korea has created "a severe situation that threatens stability on the Korean Peninsula and in northeast Asia," South Korean President Roh Moo-hyun told journalists.

He said the test would make it difficult for Seoul to maintain its efforts to strengthen ties with its Communist neighbour.

"This is a warning as well as my prediction," Roh said. "Under this situation, it's difficult for South Korea to maintain engagement policy."

China expresses 'resolute opposition'

News of the test followed a demand from China and Japan on Sunday that the Communist country scrub the test.

North Korea said early last week that it would test an atomic weapon because of "the U.S. extreme threat of a nuclear war."

Following that statement, the UN, U.S. and other countries all asked that it not proceed.

China, a longtime North Korea supporter and host of stalled international talks to persuade the fellow Communist country to give up its nuclear ambitions, strongly condemned the act.

"China expresses its resolute opposition," the Chinese Foreign Ministry said. The North "defied the universal opposition of international society and flagrantly conducted the nuclear test."

North Korea is believed to have enough plutonium for as few as four and as many as about a dozen nuclear bombs. But until Monday's reported action, Pyongyang had never tested a device.

In 1996, France detonated a bomb beneath Fangataufa Atoll about 750 miles southeast of Tahiti that had a yield of about 120,000 tons of TNT.

The U.S. Geological Survey said it recorded a magnitude-4.2 seismic event in northeastern North Korea. Asian neighbors also said they registered a seismic event, but only Russia said its monitoring services had detected a nuclear explosion.

No one has reported detecting any radiation.

"We know the exact site of the test. The ecological situation is normal, including on Russian territory in Primorye," Defense Minister Sergei Ivanov said, referring to the Russian Far East province that shares a short border with North Korea.

Interfax, citing an unnamed diplomatic source in Moscow, said that the North Korean Foreign Ministry had informed the Russian ambassador in Pyongyang about the test two hours before it was conducted. The report could not immediately be confirmed.

"We will also impose sanctions on them," Ahmadinejad told reporters in response to a question about a decision by the five Security Council permanent members plus Germany to discuss the prospect of sanctions.

"In the past 27 years they have always threatened us with sanctions and during this time they did everything they could," he said, according to the student ISNA and semi-official ILNA agencies. "They do their thing and in return we will do ours."

Iran also called the threat of international sanctions over its disputed nuclear program a "rusty" weapon and repeated that it would not abandon uranium enrichment.

"Both officials and people in Iran have always viewed threats of sanctions as a rusty and derelict weapon," Foreign Ministry spokesman Mohammad Ali Hosseini said at a weekly news briefing Sunday. "They are accustomed to the threats."

Senior US official Nicholas Burns has said the so-called "5+1" group will start drafting a sanctions resolution this week, although he has admitted finding a consensus on the extent of punitive measures will be difficult.

But it remains to be seen whether drafting the resolution will continue immediately amid the growing uproar over the announcement by North Korea early Monday it had conducted its first test of a nuclear weapon.

The UN Security Council was expected to hold an emergency meeting later Monday to weigh how to respond to North Korea's test, which came in brazen defiance of a previous UN resolution.

Such moves could take up precious time that was to be devoted to the Iranian nuclear issue and further stave off the threat of UN action. - Agencies

Five years into the US-led war in Afghanistan, the country is far from won over, or even safely on the path to stability and democracy.

More than 3,000 people have been killed in rising violence this year. Suicide bombers are targeting ordinary Afghans and Western troops. Militants are assassinating key political figures, burning down schools, and using roadside bombs to deadly effect.

The 40,000 US and NATO troops appear further away from bringing stability than they did three years ago when their number was 2 1/2 times smaller. And Osama bin Laden, whose presence here was a trigger for the US-led attack, is still at large.

That Afghanistan's future would still remain in doubt was almost unthinkable when the US-led rout of the Taliban began on Oct. 7, 2001. The military campaign that captured Kabul, the capital, in just over a month resulted in a wave of optimism across Afghanistan, a country that had known little except war for a quarter-century.

Emerging from the Taliban's repression, the nation embraced renewed freedoms. Millions of Afghans voted for a new president in 2004 and a parliament in 2005.

But despite billions plowed into roads, clinics, and schools, development lags in the ethnic Pashtun areas in the south and east, and corruption has helped the Taliban to take root once again.

When 8,000 NATO troops moved to the border area this year to extend the government's control, they were surprised by the intensity of the resistance, often in pitched battles.

More than 3,000 people, mostly militants, have been killed nationwide in 2006, according to an Associated Press count, based on reports from US, NATO, and Afghan officials. The tally, also including Afghan security forces, officials, and civilians, is about 1,500 more than the toll for all of 2005.

The Army recruited 80,635 soldiers, roughly 7,000 more than last year. Of those, about 70,000 were first-time recruits who had never served before.

According to statistics obtained by The Associated Press, 3.8 percent of the first-time recruits scored below certain aptitude levels. In previous years, the Army had allowed only 2 percent of its recruits to have low aptitude scores. That limit was increased last year to 4 percent, the maximum allowed by the Defense Department.

The Army said all the recruits with low scores had received high school diplomas. In a written statement, the Army said good test scores do not necessarily equate to quality soldiers. Test-taking ability, the Army said, does not measure loyalty, duty, honor, integrity or courage.

Daniel Goure, vice president of the Lexington Institute, a private research group, said there is a "fine balance between the need for a certain number of recruits and the standards you set.''

"Tests don't tell you the answer to the most critical question for the Army, how will you do in combat?'' Goure said. But, he added, accepting too many recruits with low test scores could increase training costs and leave technical jobs unfilled.

"The absolute key for the Army is a high-school diploma,'' Goure said.

About 17 percent of the first-time recruits, or about 13,600, were accepted under waivers for various medical, moral or criminal problems, including misdemeanor arrests or drunk driving. That is a slight increase from last year, the Army said.

Of those accepted under waivers, more than half were for "moral'' reasons, mostly misdemeanor arrests. Thirty-eight percent were for medical reasons and 7 percent were drug and alcohol problems, including those who may have failed a drug test or acknowledged they had used drugs.

The Army said the waiver process recognizes that people can overcome past mistakes and become law abiding citizens.

Army Brig. Gen. Anthony A. Cucolo said that adding more recruiters enabled the Army to identify more recruits. "We got the right people in the field in the right places in the right numbers,'' said Cucolo, the chief spokesman for the Army.

About two-thirds of the recruits qualified for a bonus - an average of $11,000 each. Some in highly valued specialties, such as special operations forces, can get up to $40,000 in extra cash.

The Army National Guard and the Army Reserve both fell slightly short of their recruiting goals. The Reserves recruited 25,378 of the targeted 25,500; and the Guard recruited 69,042 of the targeted 70,000.