ISIS snipers, car bombs slowing advance of Iraqi troops in Tikrit

Rockets and mortars echoed across Tikrit on Thursday as Iraqi security forces clashed with Islamic State in Iraq and Syria (ISIS) militants a day after sweeping into the Sunni city north of Baghdad.

Recapturing Tikrit is seen as a key step toward rolling back the extremist group, which seized much of northern and western Iraq last summer and controls about a third of Iraq and Syria.

Iraqi troops and allied Shia militiamen entered Tikrit for the first time Wednesday from the north and south. The head of the military operation told The Associated Press on Thursday that troops would launch phase two of the offensive later in the day as they try to reach the city centre.

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The militants were trying to repel security forces with snipers, suicide car bombs, heavy machine guns and mortars, he said, speaking anonymously as he was not authorized to brief the media.

​Tikrit, the capital of Salahuddin province and birthplace of deposed former Iraqi president Saddam Hussein, sits on the Tigris River about 130 kilometres north of Baghdad. Several of Saddam's palaces remain there, and supporters of the deceased dictator are believed to have played a key role in ISIS's seizure of the city last year.

In an interview with The Associated Press on the front line, Iraqi Defense Minister Khaled al-Obeidi said he expected security forces to reach the centre of Tikrit within three to four days.

Eyes on Mosul

The operation to retake Tikrit is "essential to opening a corridor for security forces to move from the south to Mosul," he said, referring to Iraq's second-largest city and the militants' biggest stronghold.

He described the operation as "100 per cent Iraqi, from the air and ground."

Military officials said they are advancing with caution in an effort to limit damage to the city's infrastructure, so that residents can return quickly once Tikrit is retaken.

Earlier Thursday, al-Obeidi visited troops and met with senior military commanders of the Tikrit operation as well as Maj.-Gen. Qassem Soleimani, commander of the Quds Force, an elite unit of Iran's Revolutionary Guard. Soleimani and other Iranian advisers have played a key role in pushing the militants back in recent months.

The overt Iranian role and the prominence of Shia militias in the campaign have raised fears of possible sectarian cleansing should Tikrit, an overwhelmingly Sunni city, fall to the government troops.

The U.S. has said its allied coalition carrying out airstrikes targeting the extremists has not been involved in the ongoing Tikrit offensive. Iraq's Prime Minister Haider al-Abadi has appealed for more aid for his country's beleaguered ground forces, though the U.S. spent billions of dollars training and equipping Iraq's army during its eight-year occupation.