More than 100 people were killed Friday as Iraqi police and tribesmen battled Al-Qaeda-linked militants who took over parts of two Anbar provincial cities, announcing one an Islamic state.
Parts of Ramadi and Fallujah, west of Baghdad, have been held by militants for days, harkening back to the years after the 2003 US-led invasion when both cities were insurgent strongholds.
Fighting began in the Ramadi area Monday, when security forces removed the main anti-government protest camp set up after demonstrations broke out in late 2012 against what Sunni Arabs say is the marginalisation and targeting of their community.
Anger at the Shiite-led government among the Sunni minority is seen as one of the main drivers of the worst violence to hit Iraq in five years.
Police and tribesmen fought in Ramadi and Fallujah on Friday against militants from Al-Qaeda-linked group the Islamic State of Iraq and the Levant (ISIL), which operates in Iraq and Syria, security officials said.
At least 32 civilians and 71 ISIL fighters died in the clashes, the officials said, adding that they did not know how many police and tribesmen were killed.
Hundreds of gunmen, some of them carrying the black flags often flown by jihadists, gathered at outdoor weekly Muslim prayers in central Fallujah, a witness said.
One of them went to where the prayer leader had stood, and said: "We announce that Fallujah is an Islamic state and call you to stand by our side."
At least 14 people were killed on Monday and Tuesday in and near Ramadi, while the tolls from the following two days were not immediately clear.
Fallujah was the target of two major assaults after the 2003 US-led invasion, in which American forces saw some of their heaviest fighting since the Vietnam War.
American troops fought for years, aided by Sunni tribesmen in the Sahwa militia forces from late 2006, to wrest control of Anbar from militants.
During their time in Iraq, US forces suffered almost one-third of their total fatalities in Anbar, according to independent website icasualties.org.
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But two years after US forces withdrew from Iraq, the power of militants in the province is again on the rise.
Clashes erupted in the Ramadi area on Monday as security forces tore down the sprawling anti-government protest camp on a nearby highway.
The violence then spread to Fallujah, and a subsequent withdrawal of security forces from areas of both cities cleared the way for ISIL to move in.
ISIL is the latest incarnation of an Al-Qaeda affiliate that lost ground from 2006, as Sunni tribesmen and former insurgents allied with US troops against jihadists in a process that began in Anbar and came to be known as the "Awakening."
But the extremist group has made a striking comeback following the US withdrawal from Iraq and the outbreak of Syria's civil war in 2011.
Charles Lister, a visiting fellow at the Brookings Doha Center, said its "strength and territorial control and influence has been expanding in Anbar for some time, but has primarily been focused on rural desertous terrain."
The Ramadi protest camp operation pushed Sunni tribes into conflict with the government, and ISIL "has ridden this wave of popular Sunni anger," Lister said.
Prime Minister Nuri al-Maliki had long sought the closure of the protest camp, dubbing it a "headquarters for the leadership of Al-Qaeda."
But its removal has come at the cost of a sharp decline in the security situation in Anbar.
And while the camp's closure has removed a physical sign of Sunni Arab grievances, the perceived injustices that underpinned the demonstration have not been addressed.
Violence in Iraq last year reached a level not seen since 2008, when the country was just emerging from a brutal period of sectarian killings.
Sunni anger helped fuel the surge in unrest, boosting recruitment for militant groups and decreasing cooperation with security forces, while the civil war in Syria also played a role, experts say.