Libya’s coastguard has intercepted four boats carrying migrants across the Mediterranean towards Europe, a UN official has said.
Migrants said 20 people from one of the vessels went overboard earlier on Wednesday and were presumed drowned.
It is unclear what caused the migrants to go overboard, said Safa Msehli, a spokeswoman for the International Organisation for Migration.
The vessel was overcrowded, which is common for many of the rubber dinghies and dilapidated boats used to smuggle migrants.
It was the latest disaster in the Mediterranean involving migrants seeking a better life in Europe.
Seven vessels smuggling hundreds of migrants have been intercepted off Libya’s coast since Tuesday, Ms Msehli said.
About 500 migrants, including nine children and 43 women, were taken to the Mabani detention centre in Tripoli, she said.
Many of the migrants were exhausted and suffered from dehydration, she said.
There has been a sharp increase in the number of crossings from Libya in recent months.
Amnesty International has said that in the first six months of 2021, more than 7,000 people intercepted at sea were forcibly returned to detention camps in Libya.
“The situation in the central Mediterranean is a humanitarian crisis,” Ms Msehli said.
“We are in July, and already have exceeded the number of interceptions for the entire year of 2020.”
An IOM report published this month said the number of migrants and refugees who died while attempting to reach Europe by sea has more than doubled this year, compared with the first six months of 2020.
The report said at least 1,146 people died between January and June. The Central Mediterranean route between Libya and Italy is the deadliest, with 741 people dying while attempting the crossing.
The deadliest shipwreck so far this year took place on April 22 off Libya, when 130 people drowned despite the ship issuing several distress calls.
Libya has in recent years become the main transit point for migrants fleeing war and poverty in Africa and the Middle East.
The country was plunged into chaos after a Nato-backed uprising that toppled and killed dictator Muammar Qaddafi in 2011.
Rights groups and officials at UN agencies that work with migrants and refugees say survivors at detention camps have reported systematic abuse, including forced labour, beatings, rape and torture.
The abuse often accompanies efforts to extort money from families before migrants are allowed to leave Libya by boat.
Earlier in July, Libyan maritime authorities said a coastguard vessel fired warning shots at a migrant boat in the Mediterranean, in an apparent effort to stop it from crossing to Europe and endangering the lives of the people on board.