Three US marines have been wounded in an ambush in Afghanistan's southern province of Kandahar.
A US spokesman described the attack as an ambush but would not release further details about the bomb or whether the incident involved Taliban guerrillas, whose insurgency in the province has picked up in recent weeks.
The ambush came two days after former US professional football star Pat Tillman, who gave up a $3.6-million sports contract to join the military, was killed in a gun battle with suspected Taliban fighters in southeastern Afghanistan.
Afghan officials said Mr Tillman's elite Army Ranger unit killed nine Taliban fighters in the clash.
An increase in attacks has forced the United Nations to temporarily suspend operations and voter registration in Kandahar province.
The United States leads 15,500 foreign troops hunting militants in Afghanistan, while about 6,300 Nato-led peacekeepers are mainly stationed in Kabul to maintain law and order.