Three American soldiers were killed Tuesday in a roadside explosion in southern Afghanistan, according to NATO.

The soldiers were in a vehicle on patrol in the Zhari district of the Kandahar province when they were killed, said NATO spokesman Col. Thomas Collins. The spiritual heartland of the Taliban, Kandahar is one of the most volatile regions in Afghanistan. Several service members were also wounded, although the extent of their injuries was not immediately known.

A NATO spokesman initially said four US service members were killed in the bombing, but the death toll has since been revised to three.

Earlier Tuesday, a suicide bomber targeted U.S. special forces north of the Afghan capital, but there were no casualties among the troops.

Maj. Bryan Woods, a spokesman for the international alliance, says the bomber and insurgents armed with small caliber weapons attacked a Special Operation Forces convoy as it was returning to base in the northern Kapisa province on Monday.

Qais Qadri, spokesman for the Kapisa governor, said one civilian was killed in the incident.

Woods said he could not confirm the death but said the special forces returned safely to their base "after engaging the enemy."

Attacks by Taliban insurgents have increased in recent months as the fighting season moves into high gear. It has been a bloody couple of days for international forces in Afghanistan, with three Georgian soldiers killed Monday when a powerful truck bomb exploded at the gate of their outpost in neighboring Helmand province. Also Monday, in northern Kapisa province, a suicide bomber hit a U.S. Special Operation Forces convoy. There were no casualties.

The Associated Press and Reuters contributed to this report.