(Updates with U.S. military)

By Mussab Al-Khairalla

BAGHDAD, June 1 (Reuters) - Residents of a Baghdad district cowered inside their homes on Friday, too afraid to go into the streets where al Qaeda militants and rival Sunni Arab insurgents have fought fierce battles in the past two days.

It is the first time growing tensions between al Qaeda and other Sunni insurgent groups in western Anbar province, the main bastion of Sunni insurgents, have exploded into open warfare on the streets of Baghdad.

The fighting, which erupted on Wednesday and continued through Thursday, forced many residents of Amiriya in southwestern Baghdad to flee their homes. There were no reports of fighting on Friday as U.S. troops enforced a vehicle ban.

The U.S. military, which has sought to exploit the tensions, said on Friday it had helped local residents battle al Qaeda militants, who were armed with machineguns and rocket-propelled grenade launchers.

"This started as a popular uprising ... by the locals who are tired of the violence that al Qaeda has brought to the neighbourhood," Lieutenant-Colonel Dale Kuehl, commander of the 1st Battalion, Fifth Cavalry Regiment, told Reuters in an email.

In one incident, troops had come to the aid of residents besieged in a mosque by heavily armed al Qaeda militants, he said in the first U.S. military comment on the fighting.

He said he did not know the total death toll, but residents had told him at least three al Qaeda commanders had been killed. He said U.S. forces had helped at least 10 wounded people.

The fighting comes despite a major crackdown by thousands of U.S. and Iraqi troops in the capital aimed at quelling sectarian violence between Shi'ite Muslims and Sunni Arabs that has raised the spectre of civil war.

BATTLE FOR CONTROL

Residents say militants from the al Qaeda-led Islamic State in Iraq and the Islamic Army of Iraq, mainly driven by ex-army officers and supporters of the Baath party of executed former President Saddam Hussein, are fighting for control of Amiriya.

The clashes in the district died down overnight, residents said. Kuehl said al Qaeda was regrouping.

Residents said they were too afraid to go outside despite the lull in violence as militants had set up fake checkpoints to kidnap people. One resident said he was abducted for several hours on Thursday.

"I'm inside my house holding my Kalashnikov rifle with a group of friends," said another, a 22-year-old resident who also asked not to be identified.

"We're terrified because both sides are storming into houses trying to find each other. We can see from the window that some of these groups are setting up checkpoints. There are a number of bodies in the street outside."

Residents said both sides had brought in more fighters from neighbouring districts and possibly as far afield as Anbar.

Details of the fighting, which residents said began on Wednesday, are confused as journalists are unable to enter the area. A cameraman for U.S. news organisation Associated Press was shot dead near his home in Amiriya on Thursday.

The clashes are some of the clearest evidence yet of the split between al Qaeda, which is driven by foreign fighters who favour car bombs that kill indiscriminately, and other, homegrown insurgent groups fighting U.S. and Iraqi forces.

Some Sunni tribal leaders opposed to al Qaeda's ruthlessness and adherence to a hardline form of Sunni Islam have also formed the Anbar Salvation Council, a move welcomed by the U.S military which six months ago had given up the province as lost.

Al Qaeda has replied with a campaign of bombings, intimidation and political assassinations against the tribes.

(Additional reporting by Paul Tait)

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