Iraqi special forces on March 26 began what Baghdad hopes is the final push to regain control of central Tikrit from the Islamic State (IS) extremist group.
Iraqi forces advanced on central Tikrit after U.S.-led coalition jets launched their first air strikes on IS targets in Tikrit on March 25.
According to the Associated Press news agency, clashes intensified during the day as Iraqi forces moved toward the city center.
On March 26, an AP reporter heard a second round of air strikes over Tikrit.
The push, however, is going ahead without the country's Iran-backed Shi'ite militias.
The top U.S. general for the Middle East said on March 26 that Iranian-backed Shi'ite militias have left the fight and pulled back from Tikrit as a condition for U.S. involvement.
Army General Lloyd Austin, head of U.S. Central Command, told the Senate Armed Services Committee he had insisted the militias pull back before the U.S. began flying intelligence-gathering flights over the weekend and dropping bombs on March 26 in support of Iraqi soldiers and federal police.
Some militia spokesmen contested that account, saying the forces chose to withdraw to protest U.S. involvement.
Iraqi Prime Minister Haidar al-Abadi -- who requested the coalition air action -- arrived in Tikrit on March 26 to oversee operations to retake late former dictator Saddam Hussein's home city.
Islamic State militants seized predominantly Sunni Tikrit in June 2014 during their rapid advance across northern and western Iraq.
A spokesman for Iraq's Defense Ministry said on March 26 the coalition had carried out 17 strikes in Tikrit so far, in addition to 24 by Iraq's own air force.
Iraqi troops, backed by allied Shi'ite parliamentary groups, began the offensive to retake Tikrit in early March.
Iraqi forces retook the area around Tikrit in the first week of the campaign and entered some districts of the city itself.
However, IS militants have managed to hold out in several areas including a complex of palace that was built during Saddam's rule.
Austin, the U.S. general, said there were about 4,000 Iraqi forces, commandos, and police battling for the city.
With reporting by AP and Reuters