Guards at a Libyan detention center for migrants shot dead at least six people amid chaos in the overcrowded facility, U.N. officials said Saturday, the latest tragedy involving migrants in the North African country.

The development comes a week after authorities rounded up more than 5,000 migrants in a massive crackdown and after U.N.-commissioned investigators said abuses and ill treatment of migrants in Libya amount to crimes against humanity.

The shooting took place Friday in the Mabani detention center west of the capital Tripoli, where authorities earlier this month sent 4,187 new detainees, including 511 women and 60 children, according to the International Organization for Migration.

A spokesman for Libya’s Interior Ministry, which oversees migrant detention centers, did not immediately respond to requests for comment.

It wasn’t immediately clear what triggered the violence. But Vincent Cochetel, the U.N. refugee agency’s special envoy for the Central Mediterranean, said “human rights violations and inhuman conditions” at Libya’s overcrowded detention centers led to the mayhem, which included “indiscriminate shooting.”

Cochetel urged the European Union and U.N. to impose sanctions on those implicated in the abuses against migrants, especially after the U.N.-commissioned report.

“Some individuals bear special responsibility for the human rights abuses committed either because they are directly involved in them or because they cover them under their authority. It is time for the U.N. and the EU sanctions committee to take action and list some individuals,” he told The Associated Press.

Federico Soda, the head of IOM’s mission in Libya, said at least six migrants were shot dead by guards.

Footage circulated online purporting to show hundreds of migrants fleeing the detention center in an apparent mass escape through a gap in the facility fence. Some were seen helping apparent wounded fellow migrants. Other videos showed large numbers of migrants running through the streets in Tripoli.

Earlier this week, a group of migrants attempted to flee from the the Mabani center, but they were met “with extreme violence,” according to medical aid group Doctors without Borders, which was granted a rare visit to the center.

The group, also known by its French acronym MSF, said its visiting team “heard two rounds of heavy gunfire at very close range and witnessed the indiscriminate beating of a group of men who were later forced into vehicles and driven to an unknown destination.”

Of the over 5,000 migrants rounded up earlier this month, 215 were children and more than 540 were women, at least 30 of whom were pregnant, according to IOM. The crackdown, which left one migrant dead and 15 others injured, began Oct. 1 in the western town of Gargaresh, a major hub for migrants in Libya, and spread to surrounding areas.

Libyan authorities described the crackdown as a security operation against illegal migration and drug trafficking. But the Interior Ministry, which led the crackdown, made no mention of any traffickers or smugglers being arrested.

Hours before the chaos in Mabani, the U.N. refugee agency said authorities demolished many unfinished buildings and makeshift houses for migrants during the crackdown.

“The raids ... have created widespread panic and fear among asylum seekers and refugees in the capital,” the UNHCR said. Many migrants, including unaccompanied children and young mothers, have protested at the UNHCR’s Community Day Center in Tripoli, demanding evacuation from Libya.

The agency said it temporality suspended its activities in the center after two of its workers were injured.

The UNHCR has urged Libyan authorities to allow the resumption of humanitarian flights out of the country, which have been suspended for almost a year.

Libya has been engulfed in chaos since a NATO-backed uprising toppled and killed longtime dictator Moammar Gadhafi in 2011. The North African nation has since emerged as a popular, if extremely dangerous, route to Europe for those fleeing poverty and civil war in Africa and the Middle East.

Thousands of migrants have been intercepted on the Mediterranean Sea and returned to Libya’s detention centers which are rife with abuses, widespread torture and sexual violence.

Investigators commissioned by the U.N.’s human rights body said violations against migrants at sea, in detention centers and at the hands of traffickers amount to crimes against humanity.

Associated Press