Backed by helicopter gunships, US troops joined the two-day battle in the Amariyah district, according to a councilman and other residents of the Sunni district.

The fight reflects a trend that US and Iraqi officials have been trumpeting recently to the west in Anbar province, once considered the heartland of the Sunni insurgency. Many Sunni tribes in the province have banded together to fight al-Qaeda, claiming the terrorist group is more dangerous than American forces.

Three more US soldiers were reported killed in combat, raising the number of American deaths to at least 122 for May, making it the third deadliest month for Americans in the conflict. The military said two soldiers died Wednesday from a roadside bomb in Baghdad and one died of wounds inflicted by a bomb attack northwest of the capital Tuesday.

Lt Col Dale C Kuehl, commander of 1st Battalion, 5th Cavalry Regiment, who is responsible for the Amariyah area of the capital, confirmed the US military's role in the fighting in the Sunni district. He said the battles raged Wednesday and Thursday but died off at night.

Although al-Qaeda is a Sunni organisation opposed to the Shia Muslim-dominated government, its ruthlessness and reliance on foreign fighters have alienated many Sunnis in Iraq.

The US military congratulated Amariyah residents for standing up to al-Qaeda.

"The events of the past two days are promising developments. Sunni citizens of Amariyah that have been previously terrorized by al-Qaeda are now resisting and want them gone. They're tired of the intimidation that included the murder of women," Kuehl said.

A US military officer, who agreed to discuss the fight only if not quoted by name because the information was not for release, said the Army was checking reports of a big al-Qaeda enclave in Amariyah housing foreign fighters, including Afghans, doing temporary duty in Iraq.