Iraq PM announces start of operation to retake Fallujah

"We are beginning the operation to liberate Fallujah," he said in a statement. "The Iraqi flag will be raised high over the land of Fallujah."

The Joint Operations Command also issued a statement announcing the beginning of operations to take back Fallujah, an IS bastion which lies only 50 kilometres (30 miles) west of Baghdad and has been out of government control since January 2014.

On Sunday, Iraq's military warned civilians still in Fallujah - estimated to number in the tens of thousands - to leave the city.

Abadi's announcement comes at a time when Iraqi ground forces backed by US-led coalition air support are gaining territory against IS, most recently in Iraq's vast western Anbar province.

Last week. Iraqi forces pushed IS out of the western town of Rutba, located 240 miles (380 kilometres) west of Baghdad, on the edge of Anbar province. Last month, Iraqi forces cleared territory along Anbar's Euphrates river valley after the provincial capital Ramadi was declared fully liberated earlier this year.

Fallujah is still home to tens of thousands of civilians and has been under IS rule since January 2014, longer than any other territory recently retaken by Iraqi forces.

Iraqi security forces repeated calls for civilians trapped inside Fallujah to flee on Sunday, but residents say that checkpoints controlled by the extremists along all roads leading out of the city are preventing most from fleeing.

Iraq's military is also still struggling to rebuild after it largely collapsed when IS fighters overran Mosul in the summer of 2014.

Since then, successful operations against IS have largely been led by the country's powerful Shia militias or Iraq's elite counterterrorism forces closely backed by coalition airstrikes. An array of fighters — including Shia militias and counterterrorism forces — have announced they plan to take part in the Fallujah operation, but it's unclear how command and control will be exercised over the disparate groups.

US-led coalition aircraft have carried out seven airstrikes in and around Fallujah over the past week. Retaking Fallujah could help protect the Iraqi capital from IS bombings like those seen over the past two weeks, according to the Baghdad-based spokesman for the US-led coalition in Iraq, Steve Warren.

Fallujah is "a safe haven for (the Islamic State group) where they can construct their bombs and plan their operations in relatively close proximity to Baghdad," Warren said.

But despite gains on the front lines, Abadi's government must deal with deepening political and social unrest in Baghdad.

Clashes between protesters and Iraqi security forces inside Baghdad's highly fortified Green Zone compound — which houses most Iraqi government ministries and foreign embassies — left two people dead after security forces fired tear gas, water cannon and live ammunition in an attempt to disperse the crowds. Over 100 people were wounded, hospital and police officials said.