At least 50 men and women in Iraq's Anbar province were lined up and shot dead by the Islamic State (Isis), said officials on Saturday.
The mass killing happened on Friday in the village of Ras al-Maa, north of Ramadi, Anbar councilman Faleh al-Issawi said.
Islamic militants accused members of the Al Bu Nimr tribe of retaliating against them after being displaced from their homes when the group seized the Anbar town of Hit last month, al-Issawi said in an AP report.
"These killings are taking place almost on a daily basis now in the areas under the control of the Islamic State group and they will continue unless this terrorist group is stopped," al-Issawi added.
An official in the Anbar governor's office confirmed the death toll.
According to BBC News, analysts say mass killings are a very deliberate strategy by Islamic State to spread terror in their opponents.
One local official, Sabah Karhout, described the killings in Anbar province as a crime against humanity and called for more international support for Sunni tribes fighting the militants in Anbar.
US Defence Secretary Chuck Hagel said the killing of Sunni tribesmen in Iraq by Islamic State fighters was the brutal "reality of what we're dealing with" in the conflict.
On Thursday, authorities found the bodies of 48 Sunni tribesmen killed by Islamic State militants in Anbar.
Mass graves have also been found containing between 80 and 220 bodies, many from the Al Bu Nimr tribe.
The Islamic State has overrun a large part of Anbar province in its push to expand its territory, which currently current stands at about one-third of both Iraq and Syria.
Iraqi government officals as well as the US-led coalition have said that Iraqi tribes are a vital component in the fight against the Islamic State group as they are able to penetrate areas inaccessible to airstrikes and ground forces.