Iraqi government forces and their allied fighters are continuing to advance towards the centre of Tikrit as part of a major offensive to recapture the strategic city from the Islamic State of Iraq and the Levant (ISIL) group.Army and militia fighters captured part of Tikrit's northern Qadisiya district, the provincial governor said on Wednesday, while in the south of the city, a security officer said another force made a rapid push towards the centre.ISIL fighters stormed into Tikrit last June during an offensive in which they captured large swathes of northern Iraq.They have since used the complex of palaces built in Tikrit under Saddam Hussein, the executed former president, as their headquarters.More than 20,000 troops and Shia militias, supported by local Sunni tribes, launched the offensive for Tikrit 10 days ago, advancing from the east and along the banks of the Tigris river.On Tuesday they took the town of al-Alam on the northern edge of Tikrit, paving the way for an attack on the city itself.The Tikrit Military Hospital was one of the latest key installations re-captured from ISIL fighters on Wednesday.Government troops have also reportedly taken control of the oil fields in al-Ojail, another town near Tikrit.