Iraqi security forces have been waging a fierce battle with Al-Qaeda-linked militants in the lawless west of the country.
Militants have seized control of large parts of Ramadi and Fallujah, two Sunni cities in Anbar Province that were once strongholds for militants fighting against U.S. forces. Sunni tribesmen in the region have taken up arms and have been fighting on both sides.
Militants have overrun police stations, seized military posts, freed prisoners, and swept through the streets of the two cities. Government forces have pounded militant positions, but have met stiff resistance.
The heavy fighting, which has left dozens dead, comes amid mounting sectarian tensions between minority Sunnis and the Shi'ite-led government. Violence in the country has surged to levels not witnessed since 2007, during the height of sectarian fighting.
Who are the main actors in the fighting?
Several players are involved in the current fighting in Anbar Province. The Iraqi national security forces are clearly on one side, while the local Al-Qaeda branch -- known as the Islamic State in Iraq and the Levant -- and its allies are on the other.
A third group consists of Sunni tribesman. Some of the tribesmen are part of Anbar's Awakening Council, pro-government Sunni militias that have previously fought Al-Qaeda. They were formed by the U.S. military during the height of the insurgency in 2006. Other tribesmen have taken up arms against the government.
According to Hayder al-Khoei, an associate fellow at London's Chatham House, the Sunni tribesmen are on both sides of the fighting.
"You have tribal forces supporting the Iraqi security services against Al-Qaeda and you have tribal forces who are fighting against the government establishing control over the [two] cities," he says. "It's still not clear if they're fighting with Al-Qaeda or it's a separate fight to Al-Qaeda."
Why are they fighting?
The reasons for the fighting are both regional and domestic.
Khoei says part of it has come from neighboring Syria, which is embroiled in an escalating sectarian conflict.
"The spillover from Syria has galvanized Al-Qaeda and has allowed them free movement across the border from Syria to Iraq and from Iraq to Syria," he says. "That definitely has an effect in terms of Al-Qaeda's strength and ability to fight Iraqi government forces."
The fighting also has to do with the deepening domestic crisis in Iraq. Al-Qaeda has become emboldened by rising tensions between the Shi'ite-led government of Prime Minister Nuri al-Maliki and the Sunni minority, which feels marginalized by Baghdad.
According to Kamran Karadaghi, a London-based Iraqi political commentator and former chief of staff to Iraqi President Jalal Talabani, much of the current fighting is a result of the long-standing political crisis in Iraq.
"The political establishment has failed to reconcile with the Sunnis," he says. "The Sunnis are almost completely sidelined. The Sunni provinces of Iraq, especially Anbar, were once staunch opponents of federalism but now they want federalism for themselves. That shows you to what extent they're dissatisfied."
What triggered the violence?
Tensions spiked in Anbar after Sunni lawmaker Ahmad al-Alwani was arrested in Ramadi on December 28, reportedly on terrorism charges.
Days later, on December 30, Iraqi security forces broke up a yearlong sit-in being staged by Sunni protesters who complained of being marginalized by the Shi'ite-led authorities and unfairly targeted by security forces. The crackdown triggered clashes between the military and local tribesmen.
The dismantling of the Sunni protest camp also prompted 44 lawmakers, many of them Sunnis, to submit their resignations.
Protests against the government first broke out in Sunni areas of western and central Iraq in late 2012 and have continued for more than a year.
What's at stake?
The ongoing fighting could have significant implications.
Domestically, the violence will deepen tensions between the government and minority Sunnis.
Karadaghi believes this could bring Iraq to the brink of civil war and lead to the country's disintegration along sectarian lines.
"The violence will only deepen the crisis in Iraq," he says. "Without a real and genuine reconciliation and political solution, the situation will escalate and become worse and worse. It might turn into a real Sunni-Shi'ite confrontation."
Regionally, the fighting in Iraq could incite a broader Sunni-Shi'ite conflict, according to Khoei.
"In Lebanon, Syria, and Iraq, Al-Qaeda has seen resurgence in terms of support, control over territory, funds, and weapons," he says. "We are seeing Shi'ite militias from all three countries fighting Al-Qaeda and fighting Salafi militants. In Iraq, the sectarian nature of the violence is much more subtle than in Syria. We're not seeing ordinary people fighting each other and that's the big difference between Syria and Iraq."