The powerful blast also killed an Afghan interpreter and 17 Afghan citizens. The suicide bomber rammed a vehicle packed with explosives into a military convoy.
Afghan officials said the bomber stuck as the convoy was passing. But a NATO spokesman said it happened at a checkpoint in Khost City, the capital of the province of the same name.
It was the third day in a row troops were targeted by insurgents. The violence has interrupted the effort to prepare and train Afghans for the U.S.'s withdrawal in 2014.
The Associated Press contributed to this report.
