The head of the United Nations Human Rights Council believes Nigerian Islamist group Boko Haram may have murdered female captives as it retreated from the advance of a multinational task force set up to end its reign of terror.

The multinational task force is composed of soldiers from Nigeria, Niger, Chad and Cameroon, as well as Benin. It was formed in February specifically to combat Boko Haram's growing threat to the region after the Islamist group attempted to expand its terror operations to Cameroon last year.

According to the National Post, UN human rights chief Zeid Raad al-Hussein told the Council during a meeting in Geneva that the multinational task force's success in reclaiming territories from Boko Haram in northeastern Nigeria "has brought to light gruesome scenes of mass graves and further evident signs of slaughter by Boko Haram."

CNN reported last month that soldiers from Chad and Niger discovered the remains of a mass grave after retaking the town of Damasak in northeastern Nigeria. The mass grave, CNN said, contained the remains of nearly 100 people, some of whom were beheaded.

Zeid also told the Council of multiple reports of the militants murdering "their so-called 'wives' — in fact, women and girls held in slavery — and other captives."

However, he gave no further details and did not speculate as to whether the victims may have included some of the 240 Nigerian schoolgirls kidnapped by Boko Haram from a secondary school in Chibok in northern Nigeria in April 2014.

A previous report in WND quoted International Christian Concern's Africa analyst Cameron Thomas as saying that some of the abducted girls had been sold off to the militants as child brides "for as little as $12."