Smoke rises from oil wells in the Ajil field east of the city of Tikrit in the Salahuddin province, March 4, 2015. Islamic State militants have set fire to oil wells in the Ajil field east of the city of Tikrit to try to hinder aerial attacks aimed at driving them from the oilfield, a witness and military source said. Black smoke could be seen rising from oil field since Wednesday afternoon, said the witness, who accompanied Iraqi militia and soldiers as they advanced on Tikrit from the east. Picture taken March 4, 2015. REUTERS/ Mahmoud Raouf (IRAQ - Tags: CIVIL UNREST CONFLICT MILITARY ENERGY)