Iraq's Prime Minister is claiming that a key city has been retaken from ISIS

Iraqi Prime Minister Haider al-Abadi has claimed that Tikrit, a city of 260,000 and the birthplace of former Iraqi dictator Saddam Hussein, has been retaken from ISIS.

Abadi's claims have not been independently verified. And earlier reports of ISIS being dislodged from key parts of the city turned out to be untrue. On March 12th, militia leaders erroneously claimed to have retaken most of Tikrit.

The Tikrit operation is the biggest Iraqi ground offensive against ISIS so far, and the Iraqi government and its militia partners are greatly invested in it succeeding.

But if Abadi's claim turns out to be true, it would mark the first time that a majority-Sunni Iraqi city has been wrested away from the control of the jihadist group.

Sunnis are a minority in Iraq, and some members of country's Sunni community view ISIS as the most capable defender of the sect's interests. If Tikrit has in fact been retaken, it would prove that anti-ISIS ground forces - which mostly consist of Shi'ite militias aided by the Iraqi army and the Iranian Revolutionary Guards Corps - are in fact gaining ground on ISIS in areas where the group is strongest.

Earlier, AFP reported that the Salaheddin provincial government headquarters in the city had been retaken from ISIS, citing various government officials. Iraqi state television is also reporting that the city has been retaken.

The spokesman for the Badr militia, a Shi'ite militia group and political party allied with the Iraqi government and assisted by the IRGC's Quds Force, told AFP that 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.

Pro-government militias and the Iraqi military began shelling Tikrit in early March, and moved an estimated 20,000 fighters to the city. They reportedly sustained heavy losses and have had difficulty taking the city, and the anti-ISIS force's efforts had reportedly stalled by mid-March.

Qassem Suleimani, the head of the IRGC's Quds Force, also traveled to Tikrit during the campaign, highlighting its importance to anti-ISIS ground forces.

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".

Suicide bombing

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

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.

The main militias in the Popular Mobilisation forces have played a key role in successful operations against IS in multiple areas north of Baghdad, but they have also been accused of abuses including summary executions and destruction of property.

During a visit to Baghdad on Monday, UN chief Ban Ki-moon said that Iraq must "bring volunteer armed groups fighting in support of the government under government control".

"Civilians freed from the brutality of Daesh should not have to then fear their liberators," Ban said, using an Arabic acronym for IS.

Security in and around Baghdad has improved markedly during the battle against IS, in large part because the jihadists have been occupied with fighting elsewhere.

But attacks still occur, such as a suicide bombing that targeted a bus carrying Iranian pilgrims on Tuesday in the Taji area, north of the capital.

The blast killed at least four people and wounded at least 11, security and medical officials said.

There was no immediate claim of responsibility for the attack, but suicide bombings are a tactic almost exclusively employed in Iraq by Sunni extremist groups including IS, which consider Shiites to be apostates and frequently target them.