Sunni Arabs have formed their own militia to counter Shia and Kurdish forces as part of an attempt to regain influence they lost after Saddam Hussein was toppled.
The so-called Anbar Revolutionaries have emerged from a split in the anti-US insurgency.
They are a new addition to a network of militias that have thrived in Iraq's bloody chaos and are tied to the country's leading ethnic and political parties, now negotiating the formation of a coalition government after the December 15th election, the second such polls since the 2003 US invasion of Iraq.
The newly organised militia is made up mostly of Saddam loyalists, Iraqi Islamists and other nationalists leading an insurgency against US and Iraqi government forces.
Sunni officials said Sunni rebels first decided to reorganise their forces into a militia after their tactical alliance with al-Qaeda, who are also Sunnis, unravelled when al-Qaeda bombs began killing fellow Sunnis in recent months.
But a key motive behind the militia's emergence is to have a force on the ground to confront the Shia Badr Brigades, whom the Sunnis accuse of killing and torturing members of their sect in death squads sanctioned by the government, officials added.
The Anbar Revolutionaries group is likely to further hamper the Iraqi government's effort to impose its authority and curb rising sectarian strife between Shias, Sunnis and Kurds.