Iraqi Prime Minister Haider al-Abadi has ordered an investigation into allegations that Shiite militiamen massacred Sunni residents in the eastern province of Diyala, his spokesman said on Thursday.

“The prime minister has ordered an investigation into the matter,” Rafid Jaboori told AFP, without elaborating.

Witnesses and Sunni leaders have accused Shiite fighters of executing more than 70 residents on Monday after military operations to expel Islamic State terrorists from their last urban stronghold in Diyala.

The alleged massacre is said to have taken place in and around a village called Barwana, north of the town of Muqdadiyah.

On Monday, the Iraqi army and allied Shiite militia declared the liberation of Diyala after a fierce battle which they said left at least 70 dead and 400 wounded among their ranks.

Senior military officials have denied accusations of a massacre in Barwana under their watch, arguing that accounts of revenge killings by Shiite fighters were fabricated.

The United Nations’ top envoy in Iraq, Nickolay Mladenov, welcomed the announcement of an investigation.

“It is the responsibility of the government to ensure that all armed forces are under its control, that rule of law is respected and that civilians are protected in all areas of the country, including those areas recently liberated from ISIS,” he said.

AFP contributed to this report.