Iraqi government forces are reportedly close to key refinery held by IS

Iraqi government forces got within half a mile of the country's biggest refinery on Friday, the closest they have come to breaking an Islamic State siege of the facility during months of fighting, two army officers and a witness said.

Fighting raged in a village between the complex and the nearby town of Baiji, near a deserted area believed to contain roadside bombs planted by the militants that has been preventing an advance, they said.

A witness said security forces had crossed a bridge close to the refinery, 200 km north of the capital.

"Daesh (Islamic State) militants are escaping to the direction of a river. Airplanes are targeting them," said an army captain.

Islamic State fighters seized the city of Baiji and surrounded the sprawling refinery in June during a lightning campaign through northern Iraq.

The group also controls territory in neighboring Syria and has proclaimed a caliphate straddling both countries.

Iraq's army initially put up little resistance to Islamic State. But it has been helped in recent weeks by US-led airstrikes on militant positions.

Iraqi Prime Minister Haider al-Abadi sacked 26 military commanders this week for corruption and incompetence in the aftermath of Islamic State advance. In September, he retired two senior generals as part of an overhaul of the country's armed forces.

Speaking through an aide after Friday prayers, Iraq's top Shi'ite cleric Grand Ayatollah Ali-al Sistani reiterated his criticism of corruption in the military.

He also called on the government to get its finances in order, fund projects and create jobs.

(Reporting by Raheem Salman; Writing by Michael Georgy; Editing by Andrew Heavens)