The U.N. human rights chief is calling on the Security Council to increase monitoring in Libya and "take action" against rights violators following the release of a report that documents torture, beheadings and other violence in the country.

Thursday's call from Zeid Raad al-Hussein comes as investigators in his office released a 95-page report pointing to growing human rights violations in Libya over the past two years, following the NATO-backed overthrow of Moammar Gadhafi in 2011 and the division of the country largely between two rival governments.

Investigators in recent months heard from 250 victims and witnesses and received 900 complaint files.

Lawlessness has given an opening to Islamic State group militants to gain territory in Libya and provided an outlet for human traffickers to transport migrants toward Europe.