A US military spokeswoman said on Sunday that the convoy was attacked on Saturday near Gereshk in southern Helmand province.
She said the two soldiers who were injured have already returned to duty, and a "militiaman" was detained at the scene.
However, a Taliban spokesman told Aljazeera.net's correspondent in Afghanistan that 15 soldiers were killed in the attack, although he could not confirm if they were Afghan or American.
The killing came a week after a marine with the 22nd Marine Expeditionary Unit was killed when his foot patrol came under fire in southern Kandahar province.
At least 122 US soldiers have now died in Afghanistan since the US-led invasion to topple the Taliban government in November 2001.
There are more than 15,500 US-led foreign soldiers in the country who are working with Afghan army troops to hunt, capture and kill Taliban, al-Qaida and other resistance fighters.
In another development, six Afghans have been arrested in Panj Wahi province after smuggling around 80 assault rifles and ammunition in an oil tanker truck. It is thought the munitions were destined for the Taliban resistance.
"They [the government] are not only facing a challenge from the Taliban but from several prominent ex-mujahideen commanders like Atta Muhammad, Muhammad Dawood and Ismail Khan ... It seems that the government is running out of ideas politically; running out of money economically; and coming to a halt militarily"
Aljazeera.net Afghan correspondent
The arrests came after top US military commander in Afghanistan, Lieutenant General David Barno, warned the country's south is experiencing an upswing in suspected Taliban violence.
Aljazeera.net's Afghan correspondent, Hashmatolla Moslih, said the Taliban are out of the regrouping stage and have embarked on a successful campaign of guerrilla warfare.
"They are conducting and organising more operations and are being increasingly successful," he said. "The recent pictures of prisoners being tortured by US forces in Iraq made a lot of people angry here and have inspired further attacks."
Moslih added the central government in Kabul seems to have reached a dead-end.
"I think the government has expanded as far as it can. They are not only facing a challenge from the Taliban but from several prominent ex-mujahideen commanders like Atta Muhammad, Muhammad Dawood and Ismail Khan.
"These men are refusing to hand over their weapons because of the lack of security in the country. It seems that the government is running out of ideas politically; running out of money economically; and coming to a halt militarily."