Sunni Muslim tribesmen backed by Iraqi troops are fighting al Qaeda-linked militants for control of Iraq's western province of Anbar, in a critical test of strength for the Shi'ite-led government of Prime Minister Nouri al Maliki.
Dressed in black and waving al Qaeda flags, hundreds of Islamist insurgents using machine guns and pick-up trucks mounted with anti-aircraft guns yesterday battled tribesmen in the streets of the city of Ramadi.
The deployment of tribesmen against the militants was made possible by a deal tribal leaders struck with the Baghdad government late on Thursday to try to counter al Qaeda, which has seized government buildings and police stations in Ramadi and the province's other main city Falluja.
Al Qaeda's Islamic State of Iraq and the Levant (Isil) has been tightening its grip in Anbar, near the Syrian border, in recent months in a bid to create an Islamic state across the Iraqi-Syrian borders.
"Isil fighters want to keep their foothold that they have got in the past months but there is no way to let al Qaeda keeps any foothold in Anbar," said one tribal leader, who asked not to be named.
"The battle is fierce and not easy because they are hiding inside residential areas."
On Thursday Sunni Muslim fighters clashed with Iraqi troops trying to regain control of Falluja and Ramadi after police broke up a Sunni protest camp on Monday, leaving at least 13 dead.
Thousands of anti-government tribal fighters took over local government buildings in Falluja and Ramadi on Wednesday after the army pulled back in an attempt to calm the situation.
Fighting broke out on Thursday when the army tried to re-enter the cities.
Islamist militants linked to al Qaeda also stormed police stations in Anbar, seizing weapons caches, freeing dozens of prisoners and burning down the stations after chasing out the police and letting in looters.
Sunni anger at the Shi'ite-led government's crushing of the protest movement has inflamed Iraq's deep-seated sectarian tensions.
The dismantled camp in Anbar had been an irritant to Mr Maliki since it was set up a year ago by Sunnis protesting against what they see as the marginalizing of their sect.
Iraq's minority Sunnis held most positions of power under the late Saddam Hussein, and they are resentful of Shi'ite dominance since the invasion that toppled him in 2003 and led to elections that shifted the balance in favour of the majority sect.
A Sunni tribe in Anbar threatened to "set Iraq on fire" if Mr Maliki's government did not free Ahmed al Alwani, a prominent Sunni lawmaker from the Iraqiya bloc who was arrested last Saturday on terrorism charges.
Yesterday troops hammered the militants with Hellfire rockets recently sent by the United States to help the government's fight against al Qaeda's Iraq branch, which also operates with increasing strength in Syria's civil war across the border.
On Thursday evening outside Anbar a pick-up truck laden with explosives blew up on a busy commercial street in the city of Balad Ruz, 45 miles northeast of Baghdad, destroying several shops.
At least 19 people were killed and 37 were wounded, according to security and health officials.
Isil, formerly al Qaeda's affiliate in Iraq but now based in Syria, is said to be behind the suicide bombings, mostly against Shias, that made the 2013 civilian death toll in Iraq the worst in years.
While many of the bombings have been launched from across the Syrian border, the group has also exploited Sunni grievances against the Shia-led government.