Iraqi security forces and militias fought their way into Saddam Hussein's home city of Tikrit on Wednesday, advancing from the north and south in their biggest counter-offensive so far against Islamic State militants.

The provincial governor said the army and militia fighters captured part of the northern district of Qadisiya, while in the south of the Tigris river city a security officer said another force made a rapid push towards the centre.

"The forces entered Tikrit general hospital," an official at the main military operation command centre said. "There is heavy fighting going on near the presidential palaces, next to the hospital complex."

Islamic State fighters who stormed into Tikrit in June during a lightning offensive through north and central Iraq have used the complex of palaces built in Tikrit under Saddam, the executed former president, as their headquarters.

More than 20,000 troops and Iranian-backed Shi'ite Muslim militias known as Hashid Shaabi, supported by local Sunni Muslim tribes, launched the offensive for Tikrit 10 days ago, advancing from the east and along 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 governor of Salahuddin announces the purging of half of Qadisiya district, the largest of Tikrit's neighbourhoods," a statement from governor Raed al-Jubouri's office said.

The army and militia fighters raised the national flag above a military hospital in the section of Qadisiya they had retaken from the militants, security officials said.

After pausing while helicopters attacked Islamic State snipers and positions, the ground forces were progressing steadily, taking "one street every 30 minutes" the security official said. He said there was fierce fighting around Tikrit police headquarters just south of Qadisiya.

To the northwest, troops and Hashid Shaabi fighters were clashing with Islamic State militants in the city's industrial zone, he added.

RAMADI ATTACKS

If Iraq's Shi'ite-led government is able to retake Tikrit it would be the first city clawed back from the Sunni insurgents and would give it momentum in the next, pivotal stage of the campaign - to recapture Mosul, the largest city in the north.

Mosul is the biggest city held by the ultra-radical Islamic State, who now rule a self-declared cross-border caliphate in Sunni regions of Syria and Iraq.

Over the past few months Islamic State has gradually lost ground in Iraq to the army, Shi'ite militias and Kurdish peshmerga forces, backed by air strikes carried out by a US-led coalition of mainly Western and allied Arab states.

The US says Baghdad did not seek aerial backup from the coalition in the Tikrit campaign. Instead, support on the ground has come from neighbouring Iran, Washington's longtime regional rival, which has sent an elite Revolutionary Guard commander to oversee part of the battle.

In the western province of Anbar, suicide car bombers in seven vehicles attacked Iraqi army positions in the provincial capital Ramadi, about 90 km west of Baghdad, police and medical sources say.

A total of five people were killed in the attacks, including two policemen, and 19 were wounded, a medical source said, stressing that the toll was only preliminary. - Reuters