ISIS Attacks Iraqs Largest Refinery With Mortars, Gunfire... ISIS militants have launched an attack on Iraqs largest oil refinery with mortars and machine gun fire, refinery employees say. The extremist group has been gaining ground in Iraq, seizing control of territory in its mission to create an Islamic state. Al-Qaeda offshoot in Iraq offensive LIVE UPDATES Gruesome ISIS atrocities: Video shows Iraqi soldiers insulted, then executed (GRAPHIC) The Islamic State of Iraq and the Levant (ISIS) surrounded the refinery last week as it seized control of Iraqs second-largest city of Mosul. In response to the escalation in violence management at the refinery halted operations at the facility and evacuated foreign workers. The latest attack was unleashed at 0400 (0100 GMT) outside two of the facilitys main entrances, sources told Reuters. One mortar struck a spare parts warehouse and plumes of smoke were seen rising from the building. The refinery is the largest in Iraq and processes 300,000 barrels a day, providing oil for most of the northern region of the country. The ISIS has been advancing on the Iraqi capital city of Baghdad over the past week, seizing cities in the north of the country and expanding its sphere of control. The latest city to fall under the control of the militants was Tal Afar, which has a population of about 200,000 people. The city was taken just before dawn Monday, Mayor Abdulal Abdoul confirmed to AP. Residents of the occupied areas now worry they may be subject to persecution from the hardline Sunni militants. The US-trained Iraqi security forces have proved to be ineffective against the ISIS, with many abandoning their posts in the face of the advancing forces. More About ISIS Attacks 