Iraqi government forces have advanced into Tikrit on several fronts, forcing the Islamic State (IS) extremist group to fall back to the center of the city.
Reports said troops and Shi’ite militias backed by artillery, planes, and helicopters have retaken areas in the north, south, and west of Tikrit since they first entered the city on March 11.
Shi’ite militia commander Moeen al-Kadhimi told CNN television on March 12, the 11th day of the government offensive to retake Tikrit, that 75 percent of Tikrit was back in government control.
He added that the remaining 25 percent was in the hands of some 150 IS fighters.
Police Staff Major General Bahaa al-Azzawi told AFP news agency that Tikrit was "sealed off from all sides."
In an interview with the AP news agency, Defense Minister Khaled al-Obeidi said he expected security forces to reach the center of Tikrit within three to four days.
Speaking to reporters in Salaheddin Province, of which Tikrit is the capital, Obeidi also said that government forces would refrain from advancing too fast to avoid unecessary casualties.
"We are very keen for our losses to be as low as possible," he said. "Time is on our side, we have the initiative."
The militants were said to be using snipers, suicide car bombs, heavy machine guns, and mortars to try to repel the offensive.
Meanwhile, the BBC said it has seen video evidence that IS militants were using chlorine gas as a weapon in the battle.
It quoted the Iraqi government as saying small amounts of the chemical were being used in roadside bombs targeting its forces.
North of Tikrit, IS militants have blown up the Al-Fathaa bridge,one of the few road links across the Tigris River.
Police said on March 12 that its demolition ruptured oil pipelines connecting Iraq's largest refinery, at Baiji, to an export pipeline in Kurdish territory.
No casualty figures have been provided since the military launched its offensive on March 2 aimed at capturing Tikrit from the militants.
The IS group seized the hometown of late dictator Saddam Hussein, some 130 kilometers north of Baghdad, in June, after the Iraqi army collapsed in the face of a lightning advance by the militants across northern and western Iraq.
The 30,000 soldiers and militia fighters involved in the operation are not being supported by U.S.-led coalition air strikes, but Iran is helping to coordinate the force.
Obeidi, the defense minister, told AP that the operation was "essential to opening a corridor for security forces to move from the south to Mosul," Iraq's second-largest city and the militants' biggest stronghold.
He earlier met with senior military commanders of the Tikrit operation as well as with Iranian General Qassem Soleimani, commander of the Quds Force, an elite unit of Iran's Islamic Revolutionary Guards Corps (IRGC).