Story highlights At least 80 people have been killed in fighting in Falluja, an official says

Fighting is under way in Ramadi, but the number of casualties is not known

Gunmen called on worshipers to join a Qaeda-backed group

U.S. "partnering with the Iraqi government very closely," State Dept. says

Fighting is raging between al Qaeda-backed militants and Iraq's security forces for control of two key cities in the embattled Anbar province, even as a deal was in place with Sunni tribesmen to fight alongside Iraqi police against the terror group.

The renewed violence in the Sunni province has raised concern about the stability of the government amid dueling claims by the terror group and security forces over who was in control of Falluja and Ramadi.

At least 80 people were killed, roughly 60 of the casualties were members of al Qaeda, in clashes Friday across the province, a senior interior ministry official told CNN.

Some of the most significant fighting appeared to be in Falluja, where the U.S. military fought one of the bloodiest battles of the Iraq war, with militants planting al Qaeda flags on buildings.

Gunmen calling themselves the Islamic State of Iraq and Levant, formerly known as al Qaeda in Iraq, took to a stage before thousands of Sunnis following Friday prayers in Falluja.

"We call you to join us in our fight against the government of Nuri al-Maliki," one of the gunman said through a bullhorn.

More than two-thirds of the people in attendance left once the militant began to speak, according to a journalist working for CNN.

The gunmen ordered journalists not to cover their speech, threatening to kill anyone who attempted to film or record the event, according to the journalist, who is not being identified by CNN out of security concerns.

Fighting also was under way in Ramadi, police officials told CNN, but would not provide a specific number of casualties. In that area, tribal leaders have been calling on their fighters not to cover their faces so they can recognize their own people.

The violence -- pitting Sunni militants against Shiite-dominated forces -- recalls the bloody fighting at the height of the Iraq war that nearly tore the country apart.

State Department spokeswoman Marie Harf dismissed suggestions that the United States has abandoned Iraq following its withdrawal from the country in 2011.

"Let's be clear who's responsible for the violence. It's the terrorists who were behind it," she told reporters during a briefing in Washington. "That's why we are partnering with the Iraqi government very closely to fight this shared threat. At the end of the day, we can certainly help them fight it, but we also want to help them build their own capability to do so themselves."

The United States is sending weapons, including Hellfire rockets and drones, to aid them in their campaign against terrorism, officials have said.

Harf said a number of American officials on the ground in Iraq and in Washington "remain in touch with all of the different parties in Iraq. "

Meanwhile, after a deal brokered late Thursday, Sunni tribesman began fighting alongside Iraqi security forces in the province on Friday to try to tamp down the violence from Sunni militants.

The deal was comparable to a 2007 U.S. pact that saw Sunnis turn on al Qaeda, siding with American and Iraqi forces to bring about an end to the terrorism.

The latest round of violence erupted late last week following a raid by security forces on the home of prominent Sunni lawmaker Ahmed al-Alwani, one of the main organizers of the anti-government demonstrations in Anbar province.

Alwani's brother and five of his bodyguards were killed during the raid, which also left at least 16 people wounded, authorities said.

That was quickly followed by a move to close two protest camps that were established last year as part of ongoing demonstrations against the Shiite-led government, which protesters claim has marginalized the country's minority Sunni population.

A senior official with Iraq's interior ministry in Baghdad told CNN that al Qaeda has taken advantage of the security vacuum created by fighting between Iraqi forces and Sunnis.

But tensions between Sunnis and Shiites have been running high since last year when security forces raided a protest camp in Hawija. Dozens of people were killed in the raid, which was captured by local journalists.