Iraqi troops have started the final phase of an offensive to recapture Saddam Hussein's hometown of Tikrit from Islamic State, a military official says.
It comes hours after the United States launched airstrikes on the city.
The push is going ahead without the country's Iran-backed Shiite militias, which had been instrumental to the operation so far, after they backed out in a protest over the US action.
A militia spokesman, Mouin al-Kadhimy, said many of the Shiite fighters would boycott the Tikrit operation because of the "harmful" involvement of the airstrikes.
Later in the day, clashes intensified as Iraqi troops and special forces moved towards the city centre, Lt. Gen Abdul-Wahab al-Saadi said.
IS seized the Sunni city last summer during its lightning advance across northern and western Iraq.
The battle for Tikrit is seen as a key step towards eventually driving the group from Iraq's second largest city, Mosul, which is further north.
In an address late yesterday, Iraq's prime minister Haider al-Abadi said Iraqi forces began the "final phase" in the Tikrit offensive but did not acknowledge that US-led coalition forces were playing a direct role.
He said Iraqis, "and not anyone but you", will claim victory against the militant group.
At Iraq's request, the US began airstrikes on Tikrit yesterday in support of the stalled ground offensive, Lt Gen James L Terry, the commander of the US-led campaign to defeat Islamic State, said.
He said the airstrikes would "destroy Isil strongholds with precision, thereby saving innocent Iraqi lives while minimising" unintended damage to civilian structures.
The US first launched airstrikes to reinforce Iraq's embattled military in August.