US forces relied on airpower to get al-Qaeda on the run
US military officials said the American soldier was wounded in the foot and his injuries were not life-threatening.
The battle happened during a US special forces "search and destroy" operation which targeted two compounds 95km (60 miles) north of Kandahar.
Chairman of the US Joint Chiefs of Staff, General Richard Myers, said a key aim of the mission had been to take prisoners and 27 Taleban fighters had been captured in the pre-planned raid.
The clash - during one of the biggest ground operations since the start of the US military campaign in Afghanistan last October - is confirmation that, despite intensive bombing, American forces are still facing pockets of resistance from al-Qaeda and Taleban forces.
General Myers said intelligence reports prior to the raid indicated the compounds which were attacked were used by al-Qaeda leadership, although they were found to comprise mainly Taleban fighters.
US Central Command spokesman, Navy Commander Dan Keesee, said a large cache of weapons discovered in the one of the bases was destroyed by an AC-130 gunship.
Annan mission
The firefight came on the eve of a one-day visit to Afghanistan by UN Secretary General Kofi Annan, which is aimed at encouraging the interim administration in its huge task of rebuilding the war-ravaged country.
Mr Annan's deputy special representative for Afghanistan, Francesc Vendrell, has said he believes the international community should deploy more foreign troops in Afghanistan.
Voicing concern about the "hundreds of thousands of people with weapons" in Afghanistan, Mr Vendrell said the situation in the south of the country was still "unclear".
"There are various armed groups who do not respond yet to central command," he told the French news agency AFP.
UN seeks bigger force
Earlier, Mr Vendrell told the BBC that a force of 30,000 foreign troops might be needed for Afghanistan.
Current plans allow for up to 5,000 foreign peacekeepers to be deployed. At present, there are just 2,000 troops on the ground.
Mr Vendrell said the interim government needed to exert its authority beyond the capital Kabul so that it was accepted by the entire country.
The United States is currently holding 158 al-Qaeda and Taleban prisoners at a controversial temporary camp in Guantanamo Bay, Cuba.
It has halted further transfers of prisoners from Afghanistan while the facilities are upgraded.
Hundreds more are in detention in Afghanistan.
The US authorities are questioning al-Qaeda captives in an effort to track down Osama Bin Laden, wanted for the 11 September suicide attacks on New York and Washington.