Popular Mobilization
Shi'ite fighters chant slogans in al-Fatha, northeast of Baiji, Iraq, Oct. 18, 2015. Reuters/Thaier Al-Sudani

About a week after Iraqi fighters retook the town of Baiji, security forces announced they had uncovered at least 19 mass graves containing some 365 bodies of Islamic State group fighters, Agence France-Presse reported Wednesday. It was not clear how long the bodies had been buried or how the Iraqi forces were able to identify the individuals as members of the militant group, also known as ISIS.

Baiji is a town located about 112 miles south of the major Iraqi city of Mosul, which fell to ISIS militants June last year, and the town has been a site of major clashes in recent weeks. Iraqi forces, led largely by the Popular Mobilization forces, an umbrella of mostly Iran-backed Shiite groups, were able to retake the area days ago during a major anti-ISIS offensive. Baiji was once home to Iraq's largest oil refinery, but it has since been damaged as fighting has raged continuously for the past 16 months. It could take years before the refinery is functioning again, the New York Times reported shortly after the town was retaken.

Iraqi and Kurdish forces have seen a series of victories in northern Iraq against the militant group, which has established a stronghold in Iraq and Syria. At least 10 towns were recaptured by Kurdish fighters as of late last month.

The U.S. launched a joint raid with Kurdish forces on an ISIS outpost in the northern Iraqi town of Hawija Thursday, and succeeded in rescuing some 70 Kurdish hostages. A number of ISIS fighters were said to have been captured. Few details are yet available about the raid, but it marked the first confirmed on-ground American operation against ISIS in Iraq. One American soldier was reported to have died.

The militant organization has made inroads in Iraq since taking over the country's second largest city of Mosul in the summer of 2014. Obama announced U.S. forces would begin launching airstrikes against ISIS in Iraq shortly after.