A homicide car bomber attacked a U.S. base in eastern Afghanistan on Monday, collapsing a guard post with American soldiers inside, an Afghan official said. Three NATO soldiers were wounded in the attack, a military official said.

The attacker in the eastern Khost province rammed the explosives-laden car into the gates of the U.S. military base in Yaqoubi district, said Lutfullah Babakarheil, a district chief.

"There are American soldiers inside the collapsed guard room, but we do not know whether any are wounded or killed," Babakarheil said.

Sgt. 1st Class Brian Lamar, a spokesman for the U.S.-led coalition, said three soldiers serving under a separate command — NATO's International Security Assistance Force — were wounded in the explosion and were evacuated for medical care.

Lamar would not disclose the soldiers' nationalities because of strict rules set by NATO. However, the majority of international forces in Khost province are American.

Two Afghan policemen were wounded in the attack, Babakarheil said.