Iraqi forces launched a major assault on a city partially in the control of anti-government fighters in an attempt to end a protracted crisis ahead of elections.
The operation, which involved police, pro-government militiamen and Swat teams, sought to wrest back key neighbourhoods of Ramadi, the capital of Anbar province and one of two cities where the authorities recently lost swaths of territory.
Diplomats including the UN secretary general, Ban Ki-moon, have urged Baghdad to pursue political reconciliation to undercut support for militancy.
Iraq's prime minister, Nouri al-Maliki, has meanwhile blamed "diabolical" Arab countries for the unrest and focused on security operations ahead of the parliamentary elections scheduled to be held in April.
Iraqi forces backed by tribesmen moved into five Ramadi neighbourhoods on Sunday, with helicopters providing cover and firing on the sprawling district of Malaab.
According to state television, the defence ministry spokesman, Staff Lieutenant General Mohammed al-Askari, said: "The Iraqi army launched a large operation with helicopter cover against Daash, al-Qaida and terrorists in Ramadi."
A police lieutenant colonel and an AFP journalist in Ramadi confirmed the operation had begun. All of the neighbourhoods targeted lie in the south or centre of the city.
A large section of Ramadi and all of Falluja, both former insurgent bastions close to Baghdad, fell to anti-government fighters late last month. It was the first time the fighters had exercised such open control in major cities since the height of the insurgency that followed the US-led invasion of 2003.
Fighting originally erupted in the Ramadi area on 30 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.
On Sunday, Maliki said: "The world has united with us – the [UN] security council, the EU and most Arab countries, except some diabolical treacherous countries."
He did not single out any specific countries, but Iraqi officials have alleged Saudi Arabia and Qatar, in particular, have supported disaffected Sunnis in western Iraq, as they have staged anti-government protests in the past year.
Amman 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.
