The bodies of 150 members of an Iraqi tribe which fought Islamic State in Iraq and Syria (ISIS) have been found in a mass grave, security officials said on Thursday.

ISIS militants took the men from their villages to the city of Ramadi and killed them on Wednesday night and buried them, an official in a police operations center and another security official told Reuters.

In a separate case, witnesses said they found 70 corpses from the same Albu Nimr tribe near the town of Heet in the Anbar province, west of Iraq.

Most of the victims found near Heet were members of the police or an anti-ISIS force called Sahwa (Awakening).

“Early this morning we found those corpses and we have been told by some Islamic State militants that ‘those people are from Sahwa, who fought your brothers the Islamic State, and this is the punishment of anybody fighting Islamic State’,” an eyewitness said, using an alternative name for ISIS.

Tribal sheikhs from Albu Nimr say both sets of victims were among more than 300 men aged between 18 and 55 who were seized by ISIS this week.

Iraq’s government has been encouraging tribes to rise up against the extremist group that met little resistance when it swept through the country’s heartland in June.

ISIS, which declared a “caliphate” over territory it seized in Iraq and Syria, is being described as the world’s wealthiest “terror” group, earning $1 million a day from black market oil sales alone, in addition to $429 million it has looted from Mosul’s central bank.

ISIS has so far executed thousands in Iraq and Syria, targeting, in particular, ethnic and religious minorities.

On June 12, 2014, ISIS killed at least 1,700 Iraqi Air Force soldiers in an attack on Camp Speicher in Tikrit, northwest of the Iraqi capital. At the time of the attack there were between 4,000 and 11,000 unarmed cadets in the camp.

The Iraqi government blamed the massacre on both ISIS and members from the Arab Socialist Ba’ath Party – Iraq Region.

This month only, ISIS executed at least four women, including two doctors and a politician, in their northern Iraq strongholds. On September 22, ISIS executed a women’s rights activist, Samira Saleh al-Nuaimi, reportedly because she had condemned the demolition of heritage sites by ISIS on social media.

(Reuters, Al-Akhbar)