BAGHDAD -- Islamic State group militants shot to death at least 25 captive Yazidis at a prison camp in northern Iraq, a Yazidi lawmaker said Saturday, the latest mass killing carried out by the extremists targeting the sect.

The killings took place at a prison camp near the town of Tal Afar, some 150 kilometres (90 miles) east of the Syrian border or 420 kilometres (260 miles) northwest of Baghdad, legislator Mahma Khalil said.

Khalil said he spoke to four different people with knowledge of what happened inside of the camp, though a reason for the killings still wasn't 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 the Islamic State group captured the northern Iraqi town of Sinjar, near the Syrian border. But hundreds were taken captive by the group, with some Yazidi women forced into slavery, according to international rights groups and Iraqi officials.

About 50,000 Yazidis -- half of them children, according to U.N. figures -- fled to the mountains outside Sinjar during the onslaught. Some still remain there.

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.