Iraqi government forces are edging closer to recapturing the country’s biggest oil refinery at Baiji.

It is the nearest they have come to breaking a siege by Islamic State militants during two months of fighting.

The Iraqi soldiers advance has been halted by a series of roadside bombs believed to have been planted by the militants between the complex and the nearby town.

On Thursday, the group released an audio recording of its leader Abu Bakr al-Baghdadi to counter claims that he was killed or wounded in an air strike last week.

Some have blamed the Iraq soldiers’ slow advance on corruption and incompetence within Iraq’s forces. This week the prime minister fired 26 military commanders.

Islamic State jihadists seized the city and surrounded the sprawling refinery during a lightning campaign through northern Iraq. Their hold on the city has been loosened by US-led air strikes on militant positions but many believe they remain a force to be reckoned with.