DAVOS, Switzerland - The U.N.'s top human rights official says Libya's transitional government must take control of all makeshift prisons to prevent further atrocities against detainees.

U.N. High Commissioner for Human Rights Navi Pillay says various brigades are holding as many as 8,000 prisoners in 60 detention centres around the country.

Pillay says she is particularly concerned about sub-Saharan African detainees whom the brigades automatically assume to be fighters for former Libyan leader Moammar Gadhafi.

She told The Associated Press in an interview Friday that some detainees are subject to "torture, extrajudicial executions, rape of both men and women."

Aid group Doctors Without Borders suspended its work in one city's prisons Thursday because it said torture was rampant.