A top Iranian army general has been asked to oversee the military offensive against the Islamic State (Isis) in the northern Iraqi city of Tikrit.

In what has been called an unprecedented move, the Iraqi parliament has given Iran's general Qassem Soleimani the go-ahead to coordinate the operations in Tikrit, the hometown of former dictator Saddam Hussein.

The Iranian commander, who is already in Iraq, has significant influence over the Shi'ite militias in Iraq. Soleimani is also playing a key role in the battle against the IS.

Iraqi troops launched an attack in Tikrit over the weekend to retake territories from IS militants.

"The troops advanced without resistance in al-Teen neighbourhood from the northwestern side of the city and from the south, the police academy building has been controlled which is [2km from the province]," Raed al-Jaouri, the provincial governor of Salahuddin, of which Tikrit is the capital, told Al Arabiya Al Hadath television.

The Iraqi troops have attempted to recapture Tikrit no less than five times since June last year, but have repeatedly failed. The scale of the military campaign was stepped up this time, and more than 20,000 troops joined the offensive, including Shi'ite militias.

Tikrit, which is equidistant from the national capital Baghdad and IS's central Iraqi hub of Mosul, is a strategic point for Iraqi forces and the extremists.

"[Tikrit's] liberation will mean liberating the whole province. That will show the world once again the determination of the Iraqi government to liberate its land and protect its people no matter what their religious or ethnic background might be," said Rafid Jaboori, spokesman for the Iraqi prime minister.