The fight to control Iraq's biggest province, Anbar, has intensified, with air attacks by the military killing dozens of people and the army preparing for an assault on a second city controlled by al-Qaeda linked fighters.
Missile strikes on Ramadi, capital of the western province, killed 25 people on Tuesday, according to an Iraqi Defence Ministry spokesman, while Fallujah remained deserted as residents fled the violence and the army prepared to launch an operation to regain control of it.
"It is not possible to attack [Fallujah] now" due to concerns about civilian casualties, Staff Lieutenant-General Mohammed al-Askari, a Defence Ministry spokesman, told AFP news agency.
Al-Qaeda-linked fighters belonging to the Islamic State of Iraq and the Levant (ISIL), who now control Fallujah, have warned local people that they would be targeted if they supported the Iraqi government.
Nevertheless, military reinforcements are preparing for a full-on offensive, with the help of some of the local tribal fighters.
Early on Tuesday, three loud explosions were heard outside Fallujah, a witness said, while the army deployed reinforcements.
"Today, the army sent new reinforcements, including tanks and vehicles, to an area about 15km east of Fallujah," a police captain told AFP.
Soldiers are being kept on standby while the government waits to see if the tribes allow the army to enter Fallujah.
Nouri al-Maliki, the Iraqi prime minister, has called on residents to expel ISIL fighters and stave off a military offensive.
However, Sheikh Ali al-Hammad, a senior tribal leader, told AFP on Monday that ISIL fighters had left Fallujah, and that it was now in the hands of tribesmen.
Attacking Fallujah, a Sunni-majority city, would be extremely politically sensitive, as it could further inflame tensions between members of Iraq's Sunni Arab minority and the Shia-led government.
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 immediate cause of the unrest in Anbar was the December 28 arrest of a Sunni politician sought on terrorism charges, followed by the government's dismantling of an anti-government Sunni protest camp in Ramadi.
Parts of Ramadi and all of Fallujah were seized by al-Qaeda-linked fighters last week - the first time they have exercised such open control in major cities since the height of the Sunni insurgency that followed the 2003 US-led invasion.
Overnight, security forces and allied tribesmen sought to retake south Ramadi from fighters loyal to ISIL, but the assault failed.
"Security forces and armed tribesmen tried last night to enter areas controlled by ISIL fighters in the south of the city," a police captain in Ramadi told AFP on Tuesday.
"Clashes between the two sides began about 11pm (2000 GMT) last night and continued until 6am," he said, adding that "security forces were not able to enter these areas and ISIL fighters are still in control."
Four civilians were killed and 14 wounded in the fighting, according to Ramadi Hospital's Dr Ahmed Abdul Salam, who had no casualty figures for security forces or the fighters.
Elsewhere in Iraq, a suicide bomber drove a lorry filled with explosives into a police station in the northern city of Kirkuk.
At least two people died in the attack and several others were injured.