A prominent Yazidi lawmaker in Iraq says Islamic State group militants have killed at least 25 captive Yazidis at a prison camp.

Legislator Mahma Khalil said late Saturday that the militants killed the captives on Friday in the town of Tal Afar. Khalil said he spoke to four different people with knowledge of the situation in the camp.

Khalil says the reason behind the killings was still unknown. He said: "The militants want to spread horror among them to force them to convert to Islam or to do something else."

He added that the killed captives included men, women and elderly who were kept in a camp south of Tal Afar. He believes some 1,400 other Yazidis are still held in that camp.