Iraqi forces launched a major assault Sunday on Sunni gunmen holding neighbourhoods in a city near the capital, as an Al-Qaeda-linked group urged its fighters to "creep towards Baghdad".
Personnel from the army, police and SWAT, backed by tribesmen moved into five neighbourhoods of Ramadi, the capital of Anbar province, with helicopters providing cover.
The action came as part of efforts by the security forces to wrest back control of parts of the city which fell into anti-government hands along with the entire nearby city of Fallujah three weeks ago.
The helicopters were seen firing on the sprawling district of Malaab, which is at the centre of the battle between gunmen and militants on one side, and security forces and their tribal allies on the other.
Security forces barred movement in the city as part of the operation, defence ministry spokesman Mohammed al-Askari told state television.
Jordan meanwhile said it would host a US training programme for Iraqi forces grappling with the standoff in Anbar and the worst surge in violence countrywide since 2008, which has already killed more than 650 people this month.
Diplomats including UN chief Ban Ki-moon have urged Baghdad to pursue political reconciliation to undercut support for militancy.
But with parliamentary elections due in April, Iraqi premier Nuri al-Maliki has blamed "diabolical" Arab countries for the unrest and focused on security operations.
Sunday's operation follows an offensive by elite forces in the largely rural area of Albubali, between Ramadi and Fallujah, that security officials have described as a militant stronghold.
Troops there have been held back, however, by the threat of snipers and anti-aircraft weapons, as well as poor weather that has limited movement.
PM blames 'treacherous' Arab states
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Fighting originally erupted in the Ramadi area on December 30, when security forces cleared a year-old Sunni Arab protest camp.
It spread to Fallujah, and militants moved in and seized the city and parts of Ramadi after security forces withdrew.
It marks the first time Sunni Arab anti-government fighters, including those affiliated to the Al-Qaeda-linked Islamic State of Iraq and the Levant (ISIL), have exercised such open control in major cities since the height of the insurgency that followed the US-led invasion of 2003.
ISIL chief Abu Bakr al-Baghdadi on Sunday urged his group's fighters to continue battling the security forces.
"Be the spearhead in fighting the Safavids, stay on the frontline and creep towards Baghdad and to the south, and keep the Rawafadh busy on their doorstep," he said, using pejorative terms for Iraq's Shiite majority.
Maliki on Sunday blamed "diabolical" and "treacherous" Arab countries for supporting the unrest, and insisted he was "confident that the Iraqi people will defeat terrorism".
He did not single out specific countries, but Iraqi officials have alleged Saudi Arabia and Qatar in particular have supported disaffected Sunni Arabs in western Iraq as they have staged anti-government protests in the past year.
Amman meanwhile said on Sunday it would host US training for Iraqi forces, after an American defence official said Washington was waiting for an agreement with Jordan or another country to go ahead with the programme.
Maliki told The Washington Post in an interview published on Thursday that Baghdad specifically needed US "counter-terrorism" training.
The US defence official said Washington was also preparing to ship "several thousand" M-16 and M-4 assault rifles as well as ammunition to Iraq, after having already provided missiles to Maliki's government.
In other violence in Iraq on Sunday, 12 people were killed in restive cities north of Baghdad, a day after a wave of bombings in the capital killed 25.
Among the dead were six pro-government Sunni militiamen gunned down in an early morning attack on their checkpoint near the confessionally-mixed city of Baquba. Attacks in Kirkuk, Mosul, Tikrit and Tuz Khurmatu left six others dead.