An Al-Qaeda-linked group has called on Iraqi Sunnis who have seized one city and part of another to keep battling government forces, as fighting and attacks killed 56 people.
Parts of Anbar provincial capital Ramadi and all of Fallujah have been outside government control since last week.
It is the first time the fighters have exercised such open control in major cities since the height of the insurgency that followed the 2003 US-led invasion.
"Oh Sunni people, you were forced to take up the weapon," Abu Mohammed al-Adnani, spokesman for al-Qaeda-linked group the Islamic State of Iraq and the Levant (ISIL), said in an audio recording released on Tuesday.
"Do not lay the weapon down, because if you put it down this time, the (Shia) will enslave you and you will not rise again," he urged Iraqi Sunnis, referring to the Shia-led government in Baghdad.
Overnight, security forces and allied tribesmen sought to retake south Ramadi from ISIL, but the assault failed after seven hours of fighting, a police captain said.
Later Tuesday, missile strikes in Ramadi killed 25 fighters, according to an Iraqi defence ministry spokesperson.
'Graveyard for al-Qaeda'
The army deployed reinforcements including tanks to an area about 15 kilometres east of Fallujah, police told AFP. Soldiers however would hold off on assaulting the city for now, according to the defence ministry.
Attacking the Sunni-majority city would also be extremely politically sensitive, as it would inflame already high tensions between the Sunni Arab minority and the government.
It would also be a major test for Iraqi security forces, which have yet to undertake such an operation without the backing of American troops.
Even so, Mowaffak al-Rubaie, a former Iraqi national security adviser, struck a confident note in an interview to Al Jazeera from Baghdad on Tuesday.
"Fallujah is encircled now by the Iraqi security forces and the army. There will be a real graveyard for al-Qaeda in Fallujah," he said.
"This is not a Shia-versus-Sunni fight; it is a fight between a constitutionally elected government in Baghdad and al-Qaeda terrorists in Anbar province.
The renewed unrest in Anbar was sparked last month by the arrest of a Sunni politician sought on terrorism charges, followed by the government's dismantling of an anti-government Sunni protest camp in Ramadi.