ISIL executed 70 members of a Sunni tribe allied to the government in western Iraq earlier this week, a tribal leader and the United Nations said Wednesday.

The Takfiri ISIL group (so-called Islamic State in Iraq and Levant) executed 70 members of a Sunni tribe allied to the government in western Iraq earlier this week, a tribal leader and the United Nations said Wednesday.

The victims, members of the Albu Nimr tribe, were executed on Sunday in the Tharthar area north of Ramadi, the capital of the western Anbar province, tribal elder Naim Gaoud told AFP.

"These people who were executed were the fathers and brothers of members of the police, the army... and of tribal fighters who are battling Daesh," he said, using an Arabic acronym for ISIL.

"Daesh executed them by shooting," he said.

Hatem al-Gaoud, another clan member reached by phone, said ISIL had trapped dozens of tribe members in the Khanzir area of Tharthar since the Takfiri group launched its major offensive in Iraq last year.

"They gathered them outside Khanzir and shot them all in the head," he said.

"I don't know what ISIL did with the bodies, but it is likely they buried them in mass graves near the site of the execution," he said.

The UN Mission in Iraq's human rights office said it had been able to confirm the mass execution.

"This is not the first attack on the Albu Nimr, since they have been actively opposed to ISIL," it said in an email to AFP.

Possibly as many as 300 of the tribe's members were killed around a year ago, when anti-ISIL forces were still holding out in some parts of Ramadi, which is the Albu Nimr's main hub.