Smoke rises from the Baiji oil refinery following combat between Isis militants and Iraqi forces in June. (Reuters)
Smoke rises from the Baiji oil refinery following combat between Isis militants and Iraqi forces in June. (Reuters)

Iraqi security forces have entered the country's largest oil refinery in Baiji, after months of battling Islamic State militants who had besieged it, a police colonel said on Iraqi state television.

If confirmed, the victory would be one of the most significant for Iraqi security forces since the jihadist group seized swathes of northern Iraq in a lightning offensive in June.

"The first Iraqi force, the anti-terrorism force called Mosul Battalion, entered Baiji refinery for the first time in five months," police colonel Saleh Jaber, of the Baiji refinery protection force, told Reuters.

In what it claimed to be a live broadcast, state television showed footage of the refinery from outside its walls.

"In this area, terrorists were stationed to the left and right. If God is willing, Baiji will be the main key to liberating each span of Iraq," the commander of provincial security operations, Abdel Wahab al-Sa'adi, told the broadcaster.

The victory comes after months of ferocious fighting in Baiji, which is 200km (120 miles) north of Baghdad, and the nearby refinery. The refinery had been besieged by the militants since June, and last week the Iraqi army recaptured the town, while on Sunday they announced that they had broken the siege of the refinery.

Since June, US-led air strikes have prevented Islamic State consolidating its position and seizing further territory, while in recent weeks Iraqi security forces have begun to roll back the militants in some areas.

Last week Iraqi forces retook the Adhaim Dam, one of the country's largest.

Speaking on Monday an Iraqi army brigadier announced that the Iraqi army's next target was to re-take the town of Tikrit, the second largest Iraqi city under Isis control and birthplace of dictator Saddam Hussein.

"Over the next three days, we will work on reinforcing our capacity because we are planning to clear areas on three sides of Tikrit," an army brigadier general told AFP.