Baghdad, Nov 16 (IANS): Iraqi security forces Sunday broke the Islamic State (IS) group's months-long siege to the country's largest oil refinery in Salahudin province, a provincial security source said.

"In the early morning hours, the security forces and allied tribal fighters took full control of the sprawling Baiji refinery after they secured the roads leading to the refinery buildings and met with those troops inside who have been fighting back the attacks of IS militants for more than five months," the source told Xinhua on condition of anonymity.

On Saturday, the IS militants withdrew from the perimeter of the refinery and the troops seized its western and southern gates, while teams of explosive experts began to defuse dozens of roadside bombs and mines which were planted by the extremists around the refinery, which is located outside the town of Baiji, some 200 km north of Iraq's capital Baghdad.

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 have continued.

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

The capture of Baiji would let the Iraqi security forces 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.