Members of Iraq's Shiite militias launch a rocket towards Islamic State militants on the outskirts of the city of Falluja, in the province of Anbar, Iraq, July 12, 2015. [Photo/Agencies]

BAGHDAD - Iraqi security forces and allied militias on Monday launched a major offensive to free key cities and towns seized earlier by Islamic State (IS) militants in Iraq's western province of Anbar, a military spokesman said.

"The operations to free Anbar province were launched at 5:00 am at dawn," the spokesman for the Iraqi Joint Operations Command read in a televised statement aired on the state-run Iraqiya television.

He said that the security forces and allied Shiite militias, known as Hashd Shaabi, or popular mobilization, in addition to Sunni tribesmen and federal police forces are marching toward their targets as planned.

Iraqi security forces and allied militias have been fighting for months to retake control of key cities and towns in Iraq's largest province of Anbar since the IS militants seized most of the province and tried to advance toward Baghdad, but several counter attacks by security forces and Shiite militias have pushed them back.

The security situation in Iraq has drastically deteriorated since June 2014, when bloody clashes broke out between Iraqi security forces and the IS militants.

The IS militants took control of the country's northern city of Mosul and later seized swathes of territories after Iraqi security forces abandoned their posts in Nineveh and other predominantly Sunni provinces.