KABUL, Afghanistan — Eight soldiers with the American-led military coalition were killed Saturday, making it the bloodiest day this year for Western troops fighting here.

Two were shot in an insider attack, one died in a small-arms attack and five Americans were killed when their vehicle struck a roadside bomb, according to statements from the International Security Assistance Force and Afghan officials.

The explosion that killed the five American soldiers took place in the Maiwand district in western Kandahar Province, said Jawed Faisal, a spokesman for the governor of Kandahar. The soldiers were driving toward villages from central Maiwand when they were attacked, he said. Capt. Dan Einert, a spokesman for the international coalition here, confirmed that the five soldiers were Americans.

The Taliban claimed responsibility for the insider attack in Farah Province in western Afghanistan, where an Afghan National Army soldier turned his weapon on his trainers after an argument, said Lt. Col. Hajji Dil Jan, the deputy police chief of Farah Province.