The Taliban say they have killed 20 government soldiers in an attack on a US convoy and an Afghan government post in the south of the country.
The audacious attack took place on Saturday near the town of Spin Boldak and involved around 100 Taliban fighters.
After the assault, US-led forces pursued the fighters into the surrounding hills and called in air support from Apache helicopters.
The Taliban said they suffered only two dead and two wounded in the fighting before making a tactical withdrawal.
US admits casualties
However, the US army has given a different version of events.
US military spokesman Colonel Rodney Davis confirmed on Monday that Taliban guerrillas had stepped up attacks in southern Afghanistan, and had wounded nine coalition soldiers during the Spin Boldak attack.
But he said between 22 and 24 Taliban fighters had been killed in the fighting on Saturday, and five suspects were taken into custody the following day after an arms cache was discovered.
Davis said Special Operations Forces and Afghan militia patrolled the scene of the fighting on Sunday "finding indicators of wounded enemy, including clothing, shoes, discarded equipment, expended ammunition and RPG casings".
He added there was another firefight on Sunday with five Taliban fighters who subsequently escaped.
But senior Taliban intelligence official Mullah Abdul Samad said he had taken part in the fighting and challenged the Americans to substantiate their version of events.
"If this is correct, then we challenge them to show the bodies of these Taliban fighters," he said.
The Spin Boldak attacks come at a time when the 146,000 US-led troops in Iraq are coming under almost daily assault.
But Colonel Davis said he saw no connection between the insurgent attacks in Afghanistan and the guerrilla campaign in Iraq.
"Iraq and Afghanistan are different countries. It is not the effect of that," he said.
The US-imposed Kabul government has repeatedly expressed concern about Taliban leaders co-ordinating attacks from Pakistani territory, but Islamabad says it is doing its best to secure the long border between the two countries.
In a series of attacks since Friday, five Americans and four Italian soldiers have been wounded in the country's volatile south and east.
"They could not attack without the support of Pakistan," Spin Boldak's deputy security chief Mullah Abdul Mannan said.
More than 11,000 foreign troops have been in Afghanistan since 2001, when a US-led force overthrew the Taliban whom they accused of sheltering Osama bin Laden's al-Qaeda network.