Taliban militants killed three British soldiers patrolling in southern Afghanistan on Tuesday in the first fatalities sustained by NATO forces since taking command of the insurgency-wracked region a day earlier, the British military said.

The militants fired rocket-propelled grenades and heavy machine guns at two vehicles of the NATO-led force in the north of volatile Helmand province, where nearly 4,000 British troops are deployed. A fourth soldier was seriously wounded.

Lt. Col. Kevin Stratford Wright, spokesman for the British Helmand Task Force, said the seriously wounded soldier was evacuated to a military hospital in Helmand.

"Within the British headquarters we stood in a minute of silence as a mark of respect of those who have died," he said. "But we must get one with the job."

Afghan officials reported the heavy fighting in Helmand's Musa Qala district started early Tuesday, but had no further information.

The attack came a day after the NATO's International Security Assistance Force, led by a British general, took command of the south from the U.S.-led coalition with a mission to stabilize a region wracked by a Taliban-led insurgency and the drugs trade.

At least nine British soldiers have been killed since they started deploying to Helmand in March as part of the 8,000-strong NATO-led force, which also includes Canadian, Dutch and American troops.

NATO's mission is considered the most dangerous and challenging in the Western alliance's 57-year history. It coincides with the deadliest upsurge in fighting in Afghanistan since late 2001 that has killed more than 800 people — mostly militants — since May.

Meanwhile, Afghan and U.S.-led coalition forces early Tuesday arrested four suspected Al Qaeda operatives in eastern Khost province.

Meanwhile, Afghan and U.S.-led coalition forces arrested four suspected Al Qaeda operatives in eastern Khost province early Tuesday. They were captured in a raid launched near Sewakay village, a coalition statement said. Weapons were also confiscated, it added.

The coalition did not give the suspects' nationalities. It accused them of coordinating the smuggling of explosives into Afghanistan and planning attacks against Afghan and coalition forces in the country's east.

On Monday night, police arrested two Afghans suspected of Al Qaeda links in Helmand's capital of Lashkar Gah, said Helmand police chief Ghulam Nabi Malakhel. He said documents seized from the men showed they were associated with the terror group.

With NATO taking charge in the south, the coalition, first deployed nearly five years ago to unseat the Taliban regime for harboring Usama bin Laden, now is focusing on eastern Afghanistan, where Al Qaeda and the Taliban are active.

At Monday's hand over ceremony in Kandahar, ISAF commander British Lt. Gen. David Richards warned the force would "strike ruthlessly" against Taliban rebels when necessary.

However, NATO also hopes to bring a new strategy to dealing with the Taliban rebellion: establishing bases rather than chasing militants. It is also wants to win the support of locals by creating secure zones where development can take place.

Given the level of violence, questions remain whether it can achieve the stability required to let aid workers work in a lawless and impoverished region, where about a quarter of Afghanistan's huge opium crop is grown.

The changeover in the south followed three days of intense fighting that left nearly 60 suspected Taliban fighters dead.