It said Hill, a US assistant secretary of state, would be welcome in Pyongyang if Washington sincerely wanted to uphold a joint statement agreed last September at six-party nuclear disarmament talks.

"If the United States has sincerely made a political decision to implement the joint statement, we again invite the US chief delegate to six-way talks to visit Pyongyang and explain it directly to us," a North Korean foreign ministry spokesman told the official Korean Central News Agency (KCNA).

North Korea, meeting with six-party delegates from China, Japan, Russia, South Korea, and the United States, agreed to dismantle its nuclear programme in September in return for aid and diplomatic concessions.

But in November it launched a boycott of the talks after Washington imposed sanctions aimed at curbing Pyongyang's alleged illicit financial activities, including money laundering.

In the KCNA report, monitored in South Korea by Yonhap news agency, Pyongyang threatened retaliation if Washington stepped up pressure against the communist regime.

"If the United States keeps a hostile policy and steps up pressure on us we have no other choice but to take our strongest measure to defend our sovereignty and the rights for our own survival."

Pyongyang said last year that it had nuclear weapons. Recent reports that North Korea could be preparing to test fire a ballistic missile have triggered unease in South Korea and Japan.

North Korea invited Hill to Pyongyang for unconditional talks last September but nothing came of the approach to the US envoy who has in the past said he was prepared to go to the communist country.

Since then the six-party peace process has stalled and North Korea has been preoccupied by US financial restrictions including a ban on a Macau bank which the US accused of assisting Pyongyang's in money-laundering.

North Korea has said it will stay away from further talks until Washington lift that ban which has blocked some 24 million dollars in North Korean funds, according to the US government.

The foreign ministry spokesman accused Washington of stealing the money.

"We will surely get back the money stolen by the United States," he was quoted as saying.

Hill was in Beijing and Seoul last week for talks on the nuclear standoff, during which he stressed that Washington was not prepared to make concessions to bring Pyongyang back to talks.

Some 300 riot police patrolled Montfermeil - a town of 24,000 inhabitants - overnight Wednesday, along with several firefighter units. But there was no repeat of the violence of the previous two nights.

Early in the evening, police climbed onto the roofs of public housing estates in the area, to remove potentially dangerous objects such as car tyres or stones that could be hurled at them from above.

Run-down housing estates in both suburbs were the epicentre of the riots that spread to some 300 high-immigration French towns last autumn, and relations between police and local youths remains extremely tense.

Montfermeil has been on edge since the centre-right mayor - whose home was attacked Monday - passed a tough anti-crime decree banning public gatherings of more than three youths. The measure was later blocked in the courts.

Young people from local housing estates told AFP that the trouble began Monday after police used tear gas on a woman whose son had been arrested in connection with a robbery.

The police union Alliance said the woman had "rebelled" when officers came to search her son's home and that, feeling threatened as a group of youths started climbing the stairs, they had "used tear gas to escape."

Last year's nationwide riots were fuelled by anger at racial discrimination, a lack of educational and employment prospects and police harassment.

Some 10,000 vehicles were torched and more than 3,200 people arrested in three weeks of unrest, which prompted the government to declare a national state of emergency.

Furious Royal Navy chiefs launched TWO probes last night as it emerged most of the ship's 500-strong company were on board.

The base is surrounded by a 9ft perimeter fence and guarded by security staff and scores of military police officers with alsatians.

But yesterday, armed with just workmen's overalls and the lost pass - handed to us by a concerned reader - our man gained entry after flashing the ID card over 20 yards from guards.

They waved him through and even wished him "good morning". Yet had we been terrorists, we could have caused carnage.

Within minutes our man found the quay where HMS Ocean, the Navy's largest ship, is moored for maintenance.

As ship workers and sailors filed up the gangplank, we followed them on to the warship, designed to hold 18 attack helicopters and an army of highly-trained commandos.

Two machine gun-carrying marines were checking passes. But again our man held his finger over the real workman's picture and marched in.

Once at the heart of the ship - which is on 24 hours' notice to sail anywhere in the world if a crisis breaks - he was directed by one unwitting worker to the bridge and nerve centre.

He toured the area with video gear for 15 minutes before moving to a walkway, where photographer Marc Giddings snapped him from a road.

Our reporter also saw the engine room, living quarters and anchor room. Only one sailor asked what he was doing, but he returned to hoisting a flag when told our man was a cleaner.

We finally left the ship, praised for leading the Marines' 2003 invasion of southern Iraq, and left the base as easily as we walked in.

A Navy spokesman said: "We take all breaches of security very seriously. A full investigation by the ship and the naval base has commenced."

Footage showed that ambulances rushed to the scene. The cause of the explosion was not immediately clear.

Istanbul has witnessed deadly bomb attacks in the past and the Turkish authorities have blamed Kurdish rebel groups.

Television showed people covered in blood being treated outside the building or being carried to ambulances.

CNN Turk television said the explosion occurred at a firing range located in the basement of the building.

Blasts are not uncommon in Turkey and are often the work of diverse militant groups operating in the country.

Kurdish separatists and ultra-leftist groups have claimed responsibility for past explosions, especially in Istanbul, a city of more than 12 million people straddling Europe and Asia.

Increasing numbers of young people are being drawn to these products, which are often sold with appealing fruit flavours, the agency warned.

That's partly because they are seen as sexy and partly because they are marketed as being safer than traditional cigarettes, said Douglas Bettcher, the tobacco control coordinator for the WHO.

"The idea that somehow bubbling smoke through water is going to reduce the toxins is completely false," he said.

"I mean, you put a chunk of coal at the top of the water pipe, which in itself has a number of different carcinogens and toxic products."

Products sold in health food stores

Water pipes, also known as shishas, narghiles or hubble-bubbles, and new types of "organic" or "natural" roll-your-own cigarettes are often sold in health food stores, said Bettcher.

That could lead consumers to believe they are less dangerous than conventional cigarettes.

The agency says all tobacco products are addictive, harmful and can cause death, regardless of how they are packaged and presented to the public.

The World Health Organization called for strict regulations to control the growing list of new products in a statement released on World No Tobacco Day.

It cited statistics from the Global Youth Tobacco Survey that suggested non-cigarette tobacco products are used by 11.2 per cent of adolescents in many countries, compared to 8.9 per cent for conventional smoked products.