KABUL— Four U.S. Marines were killed today when a roadside bomb struck their vehicle in western Afghanistan, driving up Western military deaths at a pace that would make August one of the deadliest months of the war.

At least 15 Western troops have been killed in Afghanistan in August. Attacks killed at least 44 U.S service members and 31 from other international military forces in July, according to military reports.

NATO declined to say exactly where the Marines were killed or immediately release other details of the attack.

Casualties among Afghans and international troops are climbing sharply as Western forces push deeper into Taliban territory ahead of Aug. 20 presidential elections. Most violence takes place in the south and east, the traditional bases of the ethnic Pashtun insurgents.

But the Taliban has also been ramping up attacks in the relatively calmer west and north.

Local officials in southern Afghanistan said today that roadside explosions and a U.S. airstrike had killed at least 15 people, including members of a family who hit a mine on their way to a wedding party.