The Islamic State (IS) militants withdrew from the perimeter of Iraq's largest oil refinery in Salahudin province on Saturday, a provincial security source said.

"The security forces and allied tribal fighters seized the western and southern gates of Baiji refinery after the withdrawal of the IS terrorist militants," the source told Xinhua on condition of anonymity.

The troops and teams of explosive experts are defusing dozens of roadside bombs and mines which were planted by the extremist militants around the refinery, which located outside the town of Baiji, some 200 km north of the Iraqi capital of Baghdad, the source said.

"It is a matter of time till the explosive experts will secure the roads, and the troops will enter the vast refinery area to meet those troops inside who have been fighting back the attacks of IS militants for months," the source added.

On Nov. 7, the security forces backed by allied militias and aircraft launched a major offensive and gained a foothold into the nearby town of Baiji after fierce clashes with the IS militants and since then, clashes and slow advance of the troops continued, while teams of explosive experts were working to defuse the roadside bombs.

Later on, the troops took control of the whole town of Baiji and moved to free the sieged refinery.

The capture of Baiji would let the Iraqi security forces to launch another major offensive to expel the IS militants from Tikrit, Saddam Hussein's hometown and the capital of Salahudin province, which has been under the control of the extremist Sunni militants since June 11.

The seizure of Salahudin province was part of June 10 drastic security deterioration in the country, when bloody clashes broke out between Iraqi security forces and Sunni militants who took control of the country's northern city of Mosul and later seized swathes of territories in Nineveh and other predominantly Sunni provinces.