A Yazidi lawmaker said Saturday that Islamic State militants shot to death at least 25 captive Yazidis at a prison in northern Iraq.

The act is the latest mass killings carried out by the extremists targeting the sect. It took place at a prison camp near the town of Tal Afar, 90 miles east of the Syrian border, legislator Mahma Khalil said.

Khalil said he spoke to four different people with knowledge of the killings inside the camp, though a motive for the killings was not immediately apparent.

"The militants want to spread horror among them to force them to convert to Islam or to do something else," Khalil said.

He added that those killed included men, women and the elderly. He said he believes some 1,400 other Yazidis are still held in that camp.

Tens of thousands of Yazidis fled in August when ISIS captured the northern Iraq town of Sinjar, near the Syrian border. Hundreds were taken captive by the militants, with some Yazidi women forced into slavery, according to international rights groups and Iraqi officials.

About 50,000 Yazidis fled the mountains outside Sinjar, during the onslaught. Half of them are children, according to U.N. figures.

The U.S. launched airstrikes and humanitarian aid drops in Iraq on Aug. 8, partly in response to the crisis on Sinjar mountain. Since then, a U.S.-led coalition of countries have conducted airstrikes across Iraq in an effort to destroy the Islamic State group, which now holds a third of both Iraq and Syria.

The Sunni militant group views Yazidis and Shiite Muslims as apostates deserving of death, and has demanded Christians either convert to Islam or pay a special tax.

Previously, the group has let go of hundreds of other Yazidis held in captivity. Iraqi and Kurdish officials said they believe the militants couldn't afford caring for the prisoners, many of whom were elderly and sick.

The Associated Press contributed to this report