Iraqi troops began a military operation on Saturday in an attempt to regain control of the northern city of Tikrit from Sunni militants.

Included in the operation are commandos, helicopters, tanks and government-supported Sunni fighters, reports Associated Press. Residents of the city have reported fighting in Tikrit. However, it isn’t known how extensive the battles are. A resident did confirm that an air strike took place during the pre-dawn hours at the University of Tikrit. He added that there was fighting to the southeast of the city as well and militants continue to patrol the area.

According to Jawad al-Bolani, a security official in the Salahuddin Operation Command, there is no set timeline for the completion of the operation and they are working to regain control of the area.

Another resident of Tikrit, Muhanad Saif al-Din, told AP that residents are leaving the city and that Tikrit has been without power and water since Friday night.