A bomb hit a U.S. military convoy in southeastern Afghanistan (search) on Wednesday, injuring three American troops and an Afghan soldier, the military said.

The bomb exploded near the injured soldiers' Humvee near Qalat, the capital of Zabul province, a U.S. military statement said.

Two of the U.S. soldiers were evacuated to the American base at Kandahar for treatment. One had shrapnel injuries and one had a possible concussion. Both were in stable condition, the statement said.

The third American and a soldier from the Afghan National Army (search) were treated at the scene for cuts.

The United States has some 17,000 troops in Afghanistan hunting remnants of the Taliban regime ousted three years ago as well as Al Qaeda (search) militants and followers of renegade warlords.

The soldiers come under regular attack in areas including Zabul, a lawless province on the Pakistani border, where U.S. forces say they have killed scores of militants this year.