More than 100 east African migrants escaped from a camp in the Libyan town of Bani Walid where they were being held hostage and tortured, international agencies and local sources said on Saturday.
The migrants from Eritrea, Ethiopia and Somalia fled on Wednesday night to a mosque in the town where they were taken in by local associations and residents.
The hospital in Bani Walid said around 20 of them were being treated for injuries from torture.
According to Doctors Without Borders (MSF), in a statement quoting witnesses, 15 migrants were killed and 25 injured during the escape, but there was no immediate confirmation from local sources.
Some of those who escaped, mostly adolescents, told MSF rescue workers that they had been held by people traffickers for up to three years.
The medical charity said seven of those hospitalised had serious gunshot wounds.
“This is another example of the ongoing horrors suffered by many migrants and refugees while transiting through Libya” MSF said, adding that “kidnapping for ransom remains a thriving business”.
Bani Walid, 170 kilometres (110 miles) southeast of the Libyan capital Tripoli, is a transit point for migrants aiming to reach Europe by boat from the coast further north.
People traffickers and kidnappers run around 20 detention centres in the town, telephoning the migrants' families to deliver ransom demands.
Since the 2011 fall and killing of longtime dictator Moamer Kadhafi, Libya has become a key launchpad for migrants making desperate bids to reach Europe.
The conflict-riven country is regularly singled out for the exploitation and ill-treatment of migrants from sub-Saharan Africa.