KABUL, Afghanistan - -Reflecting a quickening tempo of combat in Afghanistan as a U.S. troop buildup gets under way, six Western troops died Monday in or following clashes in the south and east. At least three of the dead were Americans.

It was the worst daily toll in months for the Western coalition, which will increase this year by 30,000 American troops and an additional 7,000 from allies in the North Atlantic Treaty Organization. Four of the deaths came in separate incidents in Afghanistan's restive south, where most of the newly arriving troops are expected to be deployed.

Military officials said three Americans were killed in a clash with insurgents and a fourth foreign service member, whose nationality was not immediately disclosed, died in a roadside bombing.

The other two fatalities occurred in Afghanistan's east, where many of the insurgent fighters belong to militant groups based in Pakistan's tribal areas. One Western soldier was killed in a battle Monday, and another died of wounds suffered in an earlier engagement, according to military officials. At least one of those two was French, according to the French government. Large numbers of Americans serve in the east as well.

NATO's International Security Assistance Force also disclosed Monday the death of an American service member in an attack a day earlier in the south. That followed the deaths on Saturday of a U.S. Marine and a British journalist in a roadside bomb explosion in Helmand province.

Helmand, together with neighboring Kandahar province, is considered the heartland of the insurgency. American, British, Canadian and other allied forces have been taking significant casualties in recent months in the south.

Fighting in Afghanistan often drops off with the onset of winter weather, as heavy snow accumulates in the mountain passes, hampering insurgents' ability to move fighters and weapons. But the winter has been unusually mild this year, and clashes have continued accordingly.

Most Western military casualties are caused by insurgent-planted roadside bombs, but firefights also break out regularly between foreign forces and Taliban militants. The insurgents often stage ambushes in the wake of an explosion severe enough to drive foreign troops out of their armored vehicles, or strike as soldiers are patrolling on foot.