Afterward, as the pair met with reporters, Rumsfeld said the U.S. would maintain an active interest in the effort after the handover.

There are currently 23,000 U.S. troops in Afghanistan, and Rumsfeld told reporters before arriving in Kabul from Tajikistan that top U.S. commander Lt. Gen. Karl Eikenberry would be discussing with the Kabul government whether more troops may be required.

On Monday, Britain announced it would be sending an additional 900 troops to Afghanistan.

Recent weeks have seen a resurgence in Taliban violence, and Rumsfeld said before arriving for his 11th trip to Afghanistan that there are concerns that drug trafficking is helping bankroll the militants.

30 militants killed in coalition raid

Meanwhile, the military said an estimated 30 extremists were killed by coalition and Afghan forces Tuesday in a raid in southern Afghanistan. A coalition helicopter made an emergency landing during the operation and had to be destroyed.

The raid took place in Sangin village in the volatile Helmand province, where more than 3,000 NATO-led British troops have been deploying to take over security control from U.S. forces.

The raid was conducted as part of Operation Mountain Thrust, the large-scale anti-Taliban offensive across southern Afghanistan involving more than 10,000 troops that began last month.

About 30 more civilians were wounded in the air strikes, he added.

On the other hand, the U.S. military rejected the claim as baseless.

"No, there was no civilian injured, and we have no report to support the claim," spokesperson of the coalition Tamara Lawrence told Xinhua.

The U.S. military in a press released issued on Monday said that the coalition attacks had left more than 40 extremists dead in villages 10 km away from Trinkot.

More than 1,000 people mostly Taliban-linked militants have been killed in the ongoing insurgency since the beginning of this year.

Six Britons have been killed in Helmand since the beginning of June, nearly half the military's 13 deaths in Afghanistan since 2001.

Afghanistan has been gripped in recent months by the worst violence since a U.S.-led invasion ousted the Taliban regime after the Sept. 11, 2001 attacks.

Browne told the House of Commons that commanders decided recently to move troops into northern Helmand to stabilize the province, creating the need for more soldiers.

"We have taken casualties, but we have overmatched the opposing forces every single time we have faced them," Browne said. "They have tried to block our mission and failed."

Critics have said British troops lack needed equipment, particularly helicopters, and were ill-prepared for the intensity of the violence they have faced.

In Washington, visiting British Foreign Secretary Margaret Beckett denied the NATO-led force had underestimated the degree to which Taliban insurgents would be able to create havoc five years after being driven from power.

U.S. STRIKE: 40 suspected Taliban killed

But she acknowledged there had been "perhaps a slightly stronger reaction" from the Taliban than had been anticipated. Beckett spoke during a joint news briefing with Secretary of State Condoleezza Rice after a meeting at the State Department.

Rice conceded that Afghanistan still has determined enemies but said she would take "this Afghanistan any day over the Afghanistan which we found when we, the British and others, liberated the Afghan people from one of the worst regimes of the 20th and 21st centuries."

Beckett said most of the additional British forces being sent will work on infrastructure and other projects designed to improve the daily lives of Afghans.

Many of the additional troops will remain for at least six months as NATO takes charge of the peacekeeping mission across southern Afghanistan at the end of the month, officials said.

NATO Secretary General Jaap de Hoop Scheffer welcomed the new deployment.

"This decision reflects NATO's firm resolve to continue to support Afghanistan's reconstruction and its democratic development," he said in Brussels.

NATO is increasing its force in Afghanistan from 9,700 to 16,000, with the expansion into the south to be completed by the end of July.

The alliance hopes eventually to take on eastern Afghanistan by November, completing its expansion across the country and increasing its total numbers to 21,000.

The United States has at least 21,000 troops in Afghanistan, but there has been talk of a cut of up to 20%. Many of those that remain will be incorporated into the NATO force. However, the U.S. will also maintain a combat force independent of NATO to hunt down Taliban and al-Qaeda militants.