Leaders of a Sunni tribal group in Iraq formed to fight al-Qaeda say dozens of their men were killed by US forces in a battle north of the capital, Baghdad.
The US said its forces were looking for senior al-Qaeda members
One of the leaders of the Taji Awakening Council said airstrikes killed 45 of his pro-US fighters.
The US military said coalition forces killed 25 suspected insurgents in the Taji area at the same time in an operation targeting al-Qaeda leaders.
A US statement said arms, including anti-aircraft weapons, had been found.
The statement said forces from the US-led coalition "observed several armed men in the target area [near Taji] and, perceiving hostile intent", called in airstrikes.
Ground fighting then ensued followed by more airstrikes on another nearby location.
Several large arms caches were found, including anti-aircraft weapons, US officials said. About 20 prisoners were taken and no coalition casualties were reported.
The coalition troops had been in the area on an operation targeting senior al-Qaeda leaders in central Iraq, the US statement said.
But leaders of the Taji Awakening Council gave a different version of events.
Sheikh Jassem, the head of the council, told Reuters news agency that 45 of his men had been killed by US air strikes while they were manning roadblocks.
He said the weapons the US troops found belonged to the Islamic Army, a Sunni group which has recently joined forces with the Americans.
A suicide bomber has targeted a police convoy in Kirkuk
Another council leader, Mansour Abid Salim, said his men were mistakenly hit by the airstrikes which he tried to call off.
"Right from the first attack [Tuesday night], we have continuously been contacting American commanders that they are hitting us, their friends," he told Al-Jazeera television.
An American military spokesman said the weapons found - including anti-aircraft guns, surface-to-surface missiles and roadside bomb-making components - are not the type of weapons pro-US Iraqi militias like those of the awakening councils usually have.
A number of Sunni tribal groups have formed awakening councils to help US and Iraqi government forces to fight al-Qaeda groups. Some of these self-defence militias include former insurgents.
Separately, in the northern town of Kirkuk, a suicide car bomber targeting a police convoy killed at least six people and wounded nearly 20 others, including a senior police official.