Their deaths brought to at least 647 the number of U.S. service members who have died in Afghanistan, Pakistan and Uzbekistan since the war began in 2001. Of those, at least 480 were killed in combat.

Bombs have become the militants' weapon of choice in Afghanistan, and the number of such attacks has spiked this year, as thousands of additional American troops have joined the fight. President Barack Obama has ordered 21,000 additional troops to Afghanistan and expects the total number of U.S. forces here to reach 68,000 by year's end.

That's double the number of U.S. troops in Afghanistan in 2008 but still half as many as are now in Iraq.

Pentagon figures made available Thursday showed that in June, there were 736 incidents in Afghanistan involving bombs that either detonated or were found and defused. Those that exploded killed 23 coalition troops and wounded 166 others. The May figures showed 465 bombing incidents that killed 12 foreign troops.

The June figures were nearly three times higher than the 260 bomb incidents reported in Iraq, the Pentagon said.

Elsewhere, Afghan and coalition troops battled Taliban militants who attacked a government center in Suri district of Zabul province early Thursday, police said. Fifteen insurgents were killed and another was detained, according to provincial police chief Abdul Rehman Sarjang.

He said there were no casualties among Afghan and international forces.