Irbil , Iraq ( CNN ) Iraqi forces are doubling down efforts to retake the city of Tikrit from ISIS , even uniting Sunni and Shiite fighters in the mission . The Iraqi army , along with Sunni and Shiite militiamen , attacked ISIS strongholds in the area Monday , the state-run Iraqiya TV reported . Iraqi warplanes and helicopters are also striking targets in and around Tikrit . It 's part of a wide-scale offensive ordered by Iraqi Prime Minister Haider al-Abadi on Sunday . Tikrit fell to ISIS in June of 2014 , after the group 's capture of Iraq 's second-largest city , Mosul . Tikrit is best known to Westerners as the birthplace of former Iraqi dictator Saddam Hussein . ISIS , the radical Sunni militant group , has been on a murderous campaign to establish a caliphate across swaths of Iraq and Syria . Iraqi forces approached Tikrit from several fronts , Iraqiya TV reported , engaging with ISIS north of the city at al-Alam and south of the city at al-Dour . The element of surprise probably was not a factor , as reports of Iraqi troops amassing near Tikrit were widely shared . What awaits the Iraqi army is most likely a long , hard slog and not a quick rout . Tikrit is a big city , and the army and its associated militias have had problems recapturing much smaller towns from ISIS . There have been several failed attempts to recapture Tikrit since the second half of 2014 . While Iraqi forces have gained some territory in the area , it has generally been under ISIS control for the last eight months or so . The joint Iraqi forces fighting to retake Tikrit include Iraqi troops , members of the Shia al-Hashed al-Shaabi militia , members of the Sunni Sons of Salahuddin brigades , and other Sunni tribal fighters . The offensive involves around 30,000 fighters in all . Al-Abadi , who is also commander in chief of the armed forces , said on Twitter that he will `` oversee the operation to liberate Tikrit '' from ISIS . In short , this is the biggest test for an army trying to claw back territory that fell to ISIS last summer after a string of dramatic defeats . Last June , Tikrit was the scene of the bloodiest massacre ever perpetrated by ISIS militants . They captured more than a thousand Iraqi soldiers , who laid down their arms and donned civilian clothing in an attempt to flee a base once used by U.S. forces . ISIS subsequently executed as many as 1,700 soldiers , and posted the video of the killing online . There is concern that Iraqi forces , eager for revenge , may kill combatants and civilians alike . The U.N. 's envoy to Iraq , Nickolay Mladenov , urged all armed forces in Tikrit to do their utmost to spare civilians . U.S. and other coalition troops have been conducting a crash course to retrain and upgrade the Iraqi army , and several thousand Iraqi troops have passed through the course . This offensive will tell whether that training has made a difference . The offensive also highlights the role played by neighboring Iran in the fight against ISIS . The semiofficial Iranian FARS news agency reports that Qassim Sulaimani , the commander of the elite Iranian Al-Quds Brigade , is helping oversee the operation to retake Tikrit . Iran has provided advisers , weapons and ammunition to the Iraqi government . If the offensive succeeds , it means that retaking Mosul , a city 10 times bigger , is possible . But Tikrit is almost 200 kilometers ( 124 miles ) south of Mosul , and much of the territory in between is under ISIS control . Al-Abadi has said the immediate goal is to liberate Salah ad-Din province , of which Tikrit is the capital , and then focus on adjacent Al-Anbar province , a similarly Sunni-dominated province . After that , retaking Mosul is an option . If , however , the Tikrit offensive fails , it could spell disaster for Baghdad . There will be political recriminations , the already fragile morale of the Iraqi army could collapse , the Kurdish autonomous region could decide to break from Iraq , and it would provide ISIS with a victory it has n't seen since last summer . Ben Wedeman reported from Irbil , and Mariano Castillo reported from Atlanta . CNN 's Yousuf Basil , Holly Yan , Kareem Khadder , Hamdi Alkhshali and Mohammed Tawfeeq contributed to this report .
Tikrit stages an offensive against ISIS in Iraq . ISIS has generally controlled Iraq since 2014 .