Islamic State militants have set fire to oil wells northeast of the city of Tikrit, a witness said, to obstruct an assault by Shi'ite militia fighters and Iraqi soldiers trying to drive them from the Sunni Muslim city and surrounding towns. The witness and a military source said Islamic State fighters ignited the fire at the Ajil oil field to shield themselves from attack by Iraqi military helicopters. The offensive is the biggest Iraqi forces have yet mounted against IS, which has declared an Islamic caliphate on captured territory in Iraq and Syria and spread fear across the region by slaughtering Arab and Western hostages and killing or kidnapping members of religious minorities like Yazidis and Christians. Black smoke could be seen rising from the oil field since Wednesday afternoon, said the witness, who accompanied Iraqi militia and soldiers as they advanced on Tikrit from the east. Control of oil fields has played an important part in funding Islamic State, even if it lacks the technical expertise to run them at full capacity. Before it took over Ajil last June, the field produced 25,000 barrels per day of crude that were shipped to the Kirkuk refinery to the north-east, as well as 150 million cubic feet of gas per day piped to the government-controlled Kirkuk power station. An engineer at the site, about 35 km (20 miles) northeast of Tikrit, told Reuters last July that Islamic State fighters were pumping lower volumes of oil from Ajil, fearing that their primitive extraction techniques could ignite the gas. Bombing in August damaged the Ajil field's control room, according to the U.S. Energy Information Administration. The outcome of the battle for Tikrit, best known as the home town of executed Sunni president Saddam Hussein, will determine whether and how fast the Iraqi forces can advance further north and attempt to win back Mosul, the biggest city under Islamic State rule. The army, backed by Shi'ite militia and Kurdish Peshmerga fighters, has yet to reconquer and secure any city held by Islamic State, despite seven months of air strikes by a U.S.-led coalition, as well as weapons supplies and strategic support from neighboring Iran. Tehran, not Washington, has been the key player in the current offensive, with Iranian Revolutionary Guard general Qassem Soleimani seen directing operations on the eastern flank, and Iranian-backed militia fighters leading much of the operation.
