As Iraqi forces work to secure areas near the city of Ramadi, regional officials said Monday they had discovered a mass grave, NBC News reported. Iraqi forces, with aid from American airstrikes, drove the Islamic State group from the city in late December in what the American government labeled a win against the terrorist group.

Officials said the bodies of approximately 40 civilians were found in a grave and that they expected to find additional mass graves in the capital of Anbar Province. Ramadi was held by the militant organization, also known as ISIS, for eight months after it seized control of the city from Iraqi forces.

“Once our forces clear the city from [improvised explosive devices] we will certainly discover more mass graves,” said Eed Amash, spokesman of Anbar’s Governing Council, speaking with NBC.

Mass graves have been discovered in other regions of Iraq since ISIS came to power in 2014. Over 200 bodies were found west of Baghdad in October 2014. The Sunni Albu Nimr tribe opposed ISIS, and witnesses reported men between 18 and 55 being shot at close range. Approximately 150 members of the tribe were found in a mass grave near Ramadi in 2014.

Amash told NBC News approximately 600 families were able to escape from Ramadi when ISIS took control, but others who were caught retreating were captured and later used as “human shields.”

ISIS, known for its brutal tactics, including the sexual enslavement of prisoners, took control of Ramadi in May. Iraqi forces are now faced with rebuilding a city that has no running water or electricity and was hit with over 600 U.S. airstrikes.

ISIS fighters in the region have continued fighting against Iraqi troops and tribal groups. Eleven Iraqi fighters were killed Monday near the city of Haditha in Anbar Province, the Associated Press reported. Over 30 people were reported wounded in attacks that included a suicide car bombing.