KABUL, Afghanistan — Three foreigners working for the American-led military coalition were among 12 people killed Saturday when their vehicle was targeted by a suicide car bomber, according to Afghan and American military accounts.

The three foreign victims were Americans working for DynCorp International, a military contractor, according to a company official in Kabul, who spoke on the condition of anonymity because he was not authorized to speak to the news media.

It was believed to be the worst loss of American life in a single episode this year in Afghanistan, since American forces have mostly withdrawn, leaving less than 10,000 soldiers.

The blast took place in the center of Kabul, the latest in a series of major bombings in recent weeks, but there was no immediate word on who was responsible.