(Adds details, Islamic State comments from affiliated Twitter feed)
BAGHDAD, July 16 (Reuters) - Iraqi forces have withdrawn from the militant-held northern Iraqi city of Tikrit after a new push to retake the city met heavy resistance, a soldier who fought in the battle said on Wednesday.
Government troops and allied Shi'ite volunteer fighters were forced to retreat just before sunset on Tuesday to a base four km (2.5 miles) south after coming under heavy mortar shelling and sniper fire, the sources said.
The attempt to retake Tikrit, which fell on June 12 to Sunni insurgents led by the militant Islamic State group, began two-and-a-half weeks ago.
No fighting was reported in Tikrit on Wednesday morning, according to residents.
Tikrit lies 160 km (100 miles) north of Baghdad. It is a stronghold of loyalists of the late dictator Saddam Hussein and ex-army officers who joined forces with Islamic State to take over large parts of north and west Iraq last month.
The military had attacked from the village of Awja, some 8 km south of the city, and the initial fighting on Tuesday occurred in the southern part of the city. The army retook Awja, the birthplace of Saddam, on the night of July 3, and has been trying to push north since.
The Islamic State controls territory immediately to the north of the city. The group posted photos on an affiliated Twitter feed late Tuesday of what it called "the Tikrit battle" of dead fighters from the battle that it referred to as "martyrs" and of tanks and trucks with mounted machine guns flying the trademark black and white Islamist flag. (Reporting by a reporter in Salahuddin province and Raheem Salman, writing by Maggie Fick; editing by Ralph Boulton)