Iraqi forces said they have repelled an Islamic State (Isis) attack on the country's largest oil refinery, which was re-seized by government troops last year.

IS militants breached a security perimeter around the northern Baiji complex at the weekend (11-12 April), as they moved to retake control of the strategic site.

The jihadi group posted online video footage and pictures of its fighters attacking and later walking inside the facility amid thick black smoke caused by several fires.

"Three suicide attackers were able to reach the entrances of the refinery. Two were killed but one managed to blow himself up," an army officer told AFP.

On Monday (13 April), Baghdad said its forces successfully fought back the Sunni extremists and remain in control of the site.

"The attack that began two days ago on Baiji refinery is the most violent yet," Salahuddin provincial council member Khazaal Hammad told Reuters.

"They managed to infiltrate the security cordon and enter the refinery [complex]. But the security forces and coalition air force have dealt with the advancing militants."

Almost 40 IS militants were killed in fighting, according to Kurdish media reports.

The refinery and the nearby town of Baiji have been the scene of fierce battling since IS took it over during its lightning advance into Iraq last year.

Months of fighting ensued until government forces were able to claim control of the complex and the town in November 2014.

The jihadists later re-conquered the town, leaving the Iraqi forces in control of just a single supply line to the plant.

Before the conflict, Baiji was able to refine around 310,000 barrels of oil per day, amounting to around 40% of Iraq's refining capacity.

Last week it was reported that IS lost one of its main sources of revenue, retreating from at least another three large Iraqi oil fields due to a joint military offensive by Kurdish peshmerga and government forces.