* Sunni tribesman fight off troops in western cities
* Major escalation of tension with Shi'ite-led government
* Tribal leader threatens to 'set Iraq on fire'
By Suadad al-Salhy
BAGHDAD, Jan 2 (Reuters) - Sunni Muslim fighters clashed on Thursday with Iraqi troops trying to regain control of two western cities, in a serious escalation of their confrontation with the Shi'ite-led government of Prime Minister Nuri al-Maliki.
Tension has been running high in the Sunni-dominated province of Anbar since Iraqi police broke up a Sunni protest camp on Monday, leaving at least 13 people dead.
Thousands of anti-government tribal fighters took over local government buildings in the two main cities, Falluja and Ramadi, on Wednesday after the army pulled back in an attempt to calm the situation.
Fighting broke out on Thursday, tribal leaders and security officials said, when the army tried to re-enter the cities.
"The tribesmen are now fighting the army. What is the army doing in our city and why did they come?," Sheikh Adnan al-Mehana, the head of one of the biggest tribes in Anbar, told Reuters from Ramadi by telephone.
"Today, we defeated the army and if another force will be sent, we are ready for them," he said.
Eyewitnesses said tribal fighters had formed a new group known as the Tribal Revolutionaries. They placed snipers on the tops of houses overlooking the highway leading to Ramadi after evacuating them to prevent the army from coming back.
"There are heavily reinforced troops who were sent (by Baghdad), and the tribesmen are now deployed around the city to fight these troops and cut off their way," said a prominent tribal sheikh who declined to be named.
"We cannot let this army enter our cities. They are (Shi'ite) militias, not a national army, and they are loyal to Maliki, not to the Iraqi people."
TALKS WITH AL QAEDA
Local security officials said the tribal snipers had so far kept the army troops away and forced them to retreat.
Islamist militants linked to al Qaeda have 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 looters in.
Anbar tribal leaders said talks between tribesmen and Islamist militants were taking place, to keep the al Qaeda insurgents away from the fighting.
"We are looking to prevent the government from using excessive power against us by using the excuse of al Qaeda's presence," a senior Anbar tribal leader who is familiar with the negotiations told Reuters by phone.
Sunni anger at the Shi'ite-led government's crushing of a protest movement has inflamed Iraq's deep-seated sectarian tensions. The dismantled camp in Anbar had been an irritant to Maliki since it was set up a year ago by Sunnis protesting against what they see as the marginalizing of their sect.
Mnay of Iraq's minority Sunnis, who held most positions of power under the late Saddam Hussein, are resentful of Shi'ite dominance since the U.S.-led 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 Maliki's government does not free Ahmed al-Alwani, a prominent Sunni lawmaker from the Iraqiya bloc, who was arrested on Saturday on terrorism charges.
"Our main demand is releasing Ahmed. We will set the province and Iraq on fire if he is not released by tonight," tribal leader sheikh al-Mehana said. (Additional reporting by Kamal Namaa in Falluja; Writing by Suadad al-Salhy; Editing by Rania El Gamal and Mark Trevelyan)