BREAKING: ‪#‎Iraq‬ PM declares 'liberation' of ‪#‎Tikrit‬ from ‪#‎ISIS‬

Iraqi security forces and Shi'ite paramilitary fighters hold an Islamist State flag, which they pulled down in Tikrit, March 31, 2015

Prime Minister Haider al-Abadi on Tuesday declared the "liberation" of Tikrit from the Islamic State group, after a weeks-long operation that was Baghdad's biggest yet against the jihadists.

Abadi "announces the liberation of Tikrit and congratulates Iraqi security forces and popular volunteers on the historic milestone," his official Twitter account said, referring to allied paramilitaries who have played a major role in the fighting.

And Abadi's spokesman Rafid Jaboori told that: "Iraqi forces reached the centre of Tikrit, raised the Iraqi flag and are now clearing the city."

But it was not immediately clear if resistance in the city by the Islamic State (ISIS) group had ended entirely, and the massive challenge of defusing explosives planted in roads and houses remains ahead.

Iraqi soldiers and police and Popular Mobilisation units -- paramilitary forces dominated by Shiite militias -- began the battle to retake Tikrit on March 2.

They were able to recapture towns near Tikrit and then surrounded it, but faced difficulties pushing into the city and the operation stalled.

Over the objections of militia forces, a US-led anti-IS coalition began carrying out air strikes in support of the operation, prompting some of the groups to announce they were halting offensive operations.

Iran had been the main foreign backer of the operation for several weeks, and some militiamen accused Washington of attempting to hijack their victory.

In the end, the US carried out air strikes in spite of the presence of militias and the militias took part in the recent fighting despite Washington's role.

IS spearheaded a major militant offensive that overran much of Iraq's Sunni Arab heartland last June, and large chunks of Nineveh and Anbar provinces are still under their control.

Officials : #Iraq forces retake government HQ in #Tikrit

A member of the Iraqi security forces carries his weapon as he watches smoke rise from a scene of clashes between the Iraqi army and Islamic State militants in Tikrit March 30, 2015

Iraqi forces have retaken the Salaheddin provincial government headquarters in Tikrit from the Islamic State jihadist group, a significant advance in the battle to recapture the city, officials said Tuesday.

The spokesman for the Badr militia said members of the Popular Mobilisation units -- pro-government paramilitary forces dominated by Iran-backed Shiite militias -- took part in the fighting, after some froze offensive operations last week in response to US-led air strikes.

"Iraqi forces cleared the government complex in Tikrit," an army major general said, speaking on condition of anonymity.

"The government buildings have been under our control since last night (Monday)."

It is the most significant advance in Tikrit since pro-government forces launched an operation to retake the city on March 2, their largest since IS led an offensive that overran much of the country's Sunni Arab heartland last June.

Salaheddin Governor Raad al-Juburi confirmed that the government headquarters had been retaken, saying that Iraqi flags now flew over various recaptured buildings in the city.

Badr spokesman Karim al-Nuri also said that the government headquarters was recaptured, and that Popular Mobilisation members fought alongside federal police in the operation.

Key Shiite militia forces said they were halting Tikrit operations when a US-led anti-IS coalition began air strikes in the area after weeks in which Iran was the main foreign partner in the operation.

The coalition strikes started last Wednesday, angering Shiite militiamen who accused Washington of attempting to hijack their victory.

The Pentagon conditioned its intervention on an enhanced role for regular government forces, and on Friday hailed the withdrawal from the fight of "those Shiite militias who are linked to, infiltrated by, (or) otherwise under the influence of Iran".

The coalition said it carried out three strikes in the Tikrit area from Sunday to Monday, in its most recent statement on the operation.

After giving themselves political cover by declaring that they do not want to work with each other, both sides are still taking part in the Tikrit operation.