Iraq's prime minister called Wednesday for residents of restive Anbar province to "take a stand" against anti-government fighters, as air strikes were said to have killed 50 militants.

Prime Minister Nuri al-Maliki's call came as government forces pressed an offensive against militants, including those affiliated with the Al-Qaeda-linked Islamic State of Iraq and the Levant (ISIL), who overran parts of the provincial capital Ramadi weeks ago.

Diplomats have urged Baghdad to foster political reconciliation to undercut support for the militants, but with elections looming in April, Maliki and others have taken a hard line and focused on wide-ranging security operations.

"I ask the people of the province -- the tribes, the notables, and all who live there -- to be ready to take a stand, to take serious action against those dirty people," Maliki said in his weekly televised address.

"It is time to finish this subject, and end the presence of gangs in this city, and save the people from their evil," he said, referring to the Anbar city of Fallujah, which is entirely controlled by insurgents.

Parts of Ramadi and all of Fallujah, both west of Baghdad, have been in the hands of militants for weeks, the first time insurgents have exercised such open control in Iraqi cities since the peak of the violence that followed the 2003 US-led invasion.

Air strikes launched across Anbar killed 50 militants, including foreign fighters of Arab nationality, the defence ministry said Wednesday.

Security forces "received accurate information and carried out painful and effective air strikes against terrorist gatherings in Anbar yesterday, January 21, that killed more than 50 terrorists," a ministry statement said.

Soldiers, police and SWAT forces have meanwhile joined with tribal allies in an offensive that continued Wednesday against gunmen holding several neighbourhoods of Ramadi, an AFP journalist reported.

The army said in a statement that 13 militants were killed in firefights there.

In Fallujah, meanwhile, shelling in southern and central neighbourhoods left one person dead and 10 wounded on Wednesday, a medic said.

Residents of the city blame the army for the shelling, but defence officials say the military is not responsible.

The government has changed its language in recent days from referring to all anti-government fighters in Anbar as Al-Qaeda to instead using terms such as gangs.

And while Fallujah residents and tribal sheikhs have said ISIL has tightened its grip on the city in recent days, several other militant groups and anti-government tribes have also been involved in fighting government forces in both cities in Anbar.

Iraqi security forces have recruited their own tribal allies.

More than 22,000 families displaced

The United Nations warned Tuesday of "an exponential increase in the number of displaced and stranded families", with more than 22,000 families having registered as internally displaced.

It said the actual figure was likely to be higher, as not all those who fled had registered.

It said most of the displaced had found refuge elsewhere in Anbar, but some had gone as far afield as the northern Kurdish region.

Fighting originally erupted in the Ramadi area on December 30, when security forces cleared a year-old Sunni Arab protest camp.

The violence then spread to Fallujah, as militants moved in and seized the city and parts of Ramadi after security forces withdrew.

Violence elsewhere in the country on Wednesday killed eight people, security and medical officials said.

The deadliest incident occurred in Baghdad's western outskirts, where three mortar rounds slammed into a residential neighbourhood, killing at least three people.

Attacks in and around the restive northern cities of Mosul, Tikrit and Kirkuk killed five others.

The latest violence brought to more than 700 the number of people killed so far this month, according to an AFP tally.

By comparison, fewer than 250 people died as a result of violence in all of January 2013.