The U.S. military says the bomb exploded as the convoy drove by, about 10 kilometers outside the Afghan city of Kandahar.
U.S. spokesman Colonel Jim Yonts says the exact nature of the attack is still in question and told reporters four soldiers were injured.
"Of those four service members, one of them was seriously wounded," he said. "Service members were flown to Kandahar airfield where they are receiving medical attention."
Local police say a suicide bomber with a car full of explosives hit the convoy. They say up to five soldiers may have been killed.
Colonel Yonts says the convoy was a provisional reconstruction team that typically include a few dozen military and civilian specialists working on local development projects. He says the team was supporting civilian projects for the residents of Kandahar.
"It is a sad thing when coalition forces supporting the Afghan people are attacked by someone in this nature. They are not here as combat forces. That is a sad day when things like that happen," said Colonel Yonts.
The assault is the latest in a series of suspected Taleban-led attacks against U.S. and Afghan targets in southern and eastern Afghanistan.
Since the weather began to warm in March, rebel forces have intensified their campaign against the U.S.-backed central government.
Taleban leaders have vowed to derail local and parliamentary elections scheduled for September. But Afghan officials say the violence will not affect the country's plans.
Election organizers say more than 6,000 men and women have registered as candidates for the September vote.