Iraqi security forces and Shiite fighters walk with their combat gear in the town of Hamrin in Salahuddin province March 3, 2015. Wearing military fatigues and a white turban, Shi'ite cleric Sheikh Ahmed al-Rubaei gave an eve-of-battle address to Iran-backed fighters preparing to attack Islamic State militants in Tikrit, praising them for defending their faith and urging them to fight honourably. This week's multi-pronged attack is the biggest coordinated assault on the city since the radical Islamic State fighters seized it in June, and also the clearest example of how Tehran, rather than Washington, is now playing a more important role on the battlefield in a war that sees both Iran and the United States supporting the same side against a common foe. Picture taken March 3, 2015. To match Insight MIDEAST-CRISIS/IRAQ-FRONT REUTERS/Thaier Al-Sudani (IRAQ - Tags: POLITICS CIVIL UNREST CONFLICT MILITARY)