Security forces backed by tanks Thursday battled militants in Iraq's Anbar province, where fighting has displaced thousands and sparked warnings of rights abuses and a worsening humanitarian crisis.
The UN and NGOs have warned of a lack of access for civilians to key supplies during a government blockade of Fallujah and parts of the nearby Anbar provincial capital Ramadi, which were seized by militants last week.
And Washington has piled pressure on Baghdad to focus on political reconciliation as well as military operations to resolve the standoff.
The Anbar crisis and a protracted surge in nationwide violence are among the biggest threats to face Prime Minister Nuri al-Maliki during his eight years in office, and come just months before the country's first general election in four years.
On Thursday, security forces backed by tanks engaged in heavy fighting with Al-Qaeda-linked militants in the Albubali area, between Ramadi and Fallujah, a police officer said.
"A big force last night attacked hideouts in an area of Albubali that had been turned into a stronghold for Al-Qaeda fighters and, since this morning, there have been fierce clashes between both sides involving army tanks," the officer said.
Human Rights Watch (HRW) meanwhile condemned abuses by all sides in the Anbar clashes, criticising Iraqi government forces for using what it alleged was indiscriminate mortar fire in civilian neighbourhoods, and militants for deploying in and attacking from populated areas.
"Apparently unlawful methods of fighting by all sides have caused civilian casualties and severe property damage," the New York-based group said in a statement.
Fallujah and parts of Ramadi have been outside government hands for days -- the first time militants have exercised such open control in major cities since the insurgency that followed the 2003 US-led invasion.
The Al-Qaeda-linked Islamic State of Iraq and the Levant (ISIL) has been active in the Anbar fighting, but so have anti-government tribes.
The security forces have meanwhile recruited their own tribal allies in the fighting that has raged in Anbar for over 10 days and killed more than 250 people.
HRW also echoed concerns from the UN and other NGOs that blockades of Fallujah and Ramadi were limiting access to key supplies of food, water and fuel.
The Iraqi Red Crescent said it had provided humanitarian assistance to more than 8,000 families across Anbar but that upwards of 13,000 had fled, while the UN said it had also managed to provide critical supplies.
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Some families have sought refuge in the neighbouring province of Karbala and, according to HRW, as far away as the northern Kurdish region.
In Washington, US Vice President Joe Biden called Maliki for the second time this week, mounting pressure on the Iraqi premier over the unrest.
Biden urged Maliki to "continue the Iraqi government's outreach to local, tribal, and national leaders," following the loss of Fallujah, the White House said in a statement.
Political reconciliation, military action
Spokesman Jay Carney said Washington was pressing Maliki, a Shiite, to focus on political reconciliation as well as take military action to expel militant groups from Fallujah and Ramadi.
Traffic police have returned to Fallujah's streets, some shops reopened and more cars could be seen on Wednesday, but the city was still rocked by clashes and shelling, and ISIL urged Sunnis to keep fighting the Shiite-led government.
An Iraqi military spokesman has said an assault on Fallujah was on hold for fear of civilian casualties.
Attacking the Sunni-majority city would be a significant test for Iraqi security forces, who have yet to undertake such a major operation without the backing of US troops.
It would also be extremely sensitive politically, as it would inflame already high tensions between the Sunni Arab minority and the Shiite-led government.
Fighting erupted near Ramadi on December 30, when security forces cleared a year-old Sunni Arab protest camp.
The violence spread to Fallujah, and militants moved in and seized the city and parts of Ramadi after security forces withdrew.
Iraq was also hit by violence outside of Anbar Thursday, when a car bomb near an army recruiting centre in Baghdad killed at least seven people and wounded at least 20.