BAGHDAD -- Iraq's prime minister urged Fallujah residents on Monday to expel al Qaeda militants to avoid an all-out battle in the besieged city, a sign that the government could be paving the way for an imminent military push in an attempt to rout hard-line Sunni insurgents challenging its territorial control over the western approaches to Baghdad.

The militants' seizure of Fallujah and parts of nearby Ramadi, once bloody battlegrounds for U.S. troops, has marked the most direct challenge to Prime Minister Nouri al-Maliki's government since the departure of American forces two years ago. Both the U.S. and its longtime rival Iran view the escalating conflict with alarm, with neither wanting to see al Qaeda take firmer root inside Iraq. Washington has ruled out sending in American troops but recently delivered dozens of Hellfire missiles to help bolster Iraqi forces.

Tehran signalled Monday that it is willing to follow suit, saying it is ready to help Iraq battle al Qaeda "terrorists" by sending military equipment and advisers should Baghdad ask for it. It is unclear whether Baghdad would take up the Iranian offer, made by Gen. Mohammad Hejazi, the Iranian Army deputy chief-of-staff, in comments to Iranian state media. He ruled out the sending of ground troops across the border.

Any direct Iranian help would exacerbate sectarian tensions fueling Iraq's conflict, as Iraqi Sunnis accuse Tehran of backing what they say are their Shiite-led government's unfair policies against them. Iran has the power to sway al-Maliki's political fortunes ahead of upcoming elections through its deep ties to Iraq's major Shiite factions, which have dominated government offices and security forces since the U.S.-led invasion toppled Iran's arch-foe Saddam Hussein in 2003.

Iraqi government troops have surrounded Fallujah, which was overrun by fighters from al Qaeda's Iraq branch last week. The city is just 40 miles (65 kilometres) west of the Iraqi capital, Baghdad. It is located in the vast Sunni-dominated and largely desert province of Anbar, which borders Syria, where al Qaeda-linked groups are among the most formidable fighters among the rebels trying to topple President Bashar Assad.

Al-Maliki did not say how he expects Fallujah residents and pro-government tribesmen to push out the militants. In his message, broadcast over state TV, he also urged Iraqi troops to avoid targeting residential areas. Dozens of families have begun fleeing Fallujah to nearby towns, crammed in cars loaded with their belongings.

Ahmed Ali, an Iraq researcher at the Washington-based Institute for the Study of War, cautioned that a military assault on Fallujah would likely lead to civilian casualties and "possibly invoke other violent tribal responses." It could also give al Qaeda a chance to launch attacks in other parts of the country given the concentration of forces in Anbar.

"It is important to recognize that (al Qaeda) cannot be decisively defeated in Anbar. The (Iraqi military) presence in Anbar is therefore likely to be long-term, which increases the opportunities for (al Qaeda) to exert control elsewhere in Iraq," he wrote.

The Iraqi al Qaeda group, known as the Islamic State in Iraq and the Levant, also took control of most parts of the Anbar provincial capital of Ramadi last week.

Iraqi troops have been trying to dislodge the militants from the two cities. On Sunday, fighting pitting the militant extremists against government forces and allied tribesmen in Anbar killed dozens of people, including 22 soldiers, 10 civilians and an unknown number of militants.

U.S. Secretary of State John Kerry said Sunday that Washington was "very, very concerned" by the recent fighting but would not send in American troops. Col. Steve Warren, a Pentagon spokesman, said Monday that the U.S. is expediting the delivery of 10 Scan Eagle drones and 100 Hellfire missiles, and expects they will get to Iraq in the spring. He said the U.S. is not participating in any mission planning.

Vice-President Joe Biden called Iraq's prime minister and parliamentary speaker Monday to discuss the escalating sectarian violence and its ties to al Qaeda. The White House said Biden told al-Maliki that the U.S. stands with Iraq against the local al Qaeda branch that has overrun Fallujah. The White House said al-Maliki affirmed it was important to work with Sunni groups to isolate extremists.

Biden also spoke with Parliament Speaker Osama al-Nujaifi, a Sunni leader. The White House said the two discussed ways to sustain co-operation between Sunni communities and the Shiite-led government, and that Al-Nujaifi said he's committed to fighting terrorism.

Fallujah residents said clashes continued into Monday along the main highway that links Baghdad with neighbouring Syria and Jordan.

Al Qaeda fighters and their supporters maintained control of the city centre, spreading out over the streets and surrounding government buildings. Al Qaeda black flags have been seen on government and police vehicles captured by the militants during the clashes.

The Anbar Military Command reported that Iraqi forces killed an unspecified number of militants by firing on their vehicles from the air over the village of Karma, near Fallujah. Fighters from a pro-government Sunni militia killed six militants in a firefight outside Fallujah on Monday, a police officer said.

Sporadic clashes erupted in some parts of Ramadi too, according to residents. The Anbar provincial government said three rockets struck the military operations command centre there.

All residents in Anbar talked to The Associated Press on condition of anonymity, fearing for their safety.

Lt. Gen. Rasheed Fleih, who leads the Iraqi army's Anbar Military Command, told state TV that "two to three days" are needed to push the militants out of Fallujah and parts of Ramadi.

Also Monday, militants in a speeding car attacked an Iraqi army checkpoint in the mainly Sunni Baghdad suburb of Abu Ghraib, which is near Anbar, killing two soldiers and wounding four others, according to a police officer and a medical official. All officials spoke on condition of anonymity because they were not authorized to talk to media.

The latest unrest in Anbar began on Dec. 28, when Iraqi security forces arrested a Sunni lawmaker sought on terrorism charges. Two days later, the government dismantled a months-old, anti-government Sunni protest camp, sparking clashes with militants.

Sectarian tensions in Iraq have been coming to a head for months, however. Violence spiked after the government staged a deadly crackdown on a Sunni protest camp last April. Militants have also targeted civilians, particularly in Shiite areas of Baghdad, with waves of co-ordinated car bombings and other deadly attacks.

According to the United Nations, Iraq had the highest annual death toll in 2013 since the worst of the sectarian bloodletting began to subside in 2007. The U.N. said violence killed 8,868 last year.

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Schreck reported from Dubai, United Arab Emirates. Associated Press writers Qassim Abdul-Zahra in Baghdad, Ali Akbar Dareini in Tehran, Iran, and Lolita C. Baldor in Washington contributed to this report.