Also on Saturday, two U.S. troops died in an attack in Ghazni province, according to a spokesman for NATO forces.
The attacks follow a trend of increasing violence in Afghanistan as the 2014 deadline for NATO troop withdrawal approaches. Many fear that Afghan forces will not be prepared to manage their country's security alone at that time.
Australia suffered its worst military losses since the Vietnam War last week after three troops were shot by an Afghan colleague. Australian Defense Minister Stephen Smith vowed that the nation would see its mission in Afghanistan through — a contrast with France and New Zealand's decisions to accelerate withdrawal of their troops after several deaths.
U.S. and coalition forces have suffered a slew of "insider" attacks from Afghan security counterparts. President Obama and Defense Secretary Leon Panetta have pressed the Karzai government to take steps to halt the deaths, including stepped up vetting of Afghan recruits.
Wardak province where Saturday's bombing took place is the location of the worst attack on foreign forces in the course of the Afghanistan war. In that case, 38 troops were killed last year when the Taliban shot down a transport helicopter.