Up to 150 Europe-bound migrants were missing and feared drowned on Thursday after the boats they were traveling in capsized off Libya, the coast guard and the UN refugee agency said.
Ayoub Gassim, a spokesman for Libya's coast guard, told The Associated Press that two boats carrying around 300 migrants capsized around 120 kilometers east of the capital, Tripoli. Around 137 migrants were rescued and returned to Libya, he said, and the coast guard has recovered just one body so far.
Charlie Yaxley, a spokesman for the UN refugee agency, said 147 had been saved.
"We estimate that 150 migrants are potentially missing and died at sea," he said.
"The worst Mediterranean tragedy of this year has just occurred," said UN High Commissioner for Refugees Filippo Grandi.
In January, some 117 died or went missing off Libya's coast and around 65 people drowned after their boat sank off the coast of Tunisia in May.
Grandi called on European nations to resume rescue missions in the Mediterranean, halted after an EU decision, and appealed for an end to migrant detentions in Libya.
He said safe pathways out of the North African country are needed "before it is too late for many more desperate people."
Libya is a hub for migrants, many of whom try to reach Europe in unseaworthy boats.
