Up to 150 people may have drowned in a shipwreck off the coast of Libya, the UN refugee agency says.
A further 150 people were rescued by fishermen and returned to Libya by coastguards, the UNHCR said.
It is not clear if the migrants were on one or two boats that left the Libyan town of al Khoms, some 120km (74.5 miles) east of Tripoli.
About 164 people died on the route between Libya and Europe in the first four months of 2019.
The UN has repeatedly said people rescued in the Mediterranean should not be sent back to Libya because of the conflict and the inhumane conditions in which migrants are kept, the BBC’s Imogen Foulkes reports.