The number of migrants intercepted by Libyan coastguards on their way to Europe has trebled compared with last year.
Nearly 23,600 people have been stopped or rescued since January – compared with 7,800 in the first eight months of 2020.
Monitors said there had been a recent increase in the number of Syrians trying to cross the Mediterranean via Libya.
The increase comes amid a wider surge since May as migrants took advantage of warm Mediterranean weather and reduced travel restrictions linked to Covid-19.
More than 4,900 people were intercepted in June alone, compared with just under 1,500 the year before.
The latest figures were published by the UN’s refugee agency, UNHCR, which said the migrants were stopped in 173 separate operations.
These were carried out by Libyan coast guards and the country’s General Administration for Coastal Security, which is under the interior ministry.
The EU and Italy have provided support to Libyan coast guards in an effort to reduce illegal migration to their shores.
But hundreds of people still arrived by boat on the Italian island of Lampedusa, in addition to those stopped by Libyan guards.
The Euro-Mediterranean Human Rights Monitor said 30 migrants who recently went missing on a capsized boat had mostly come from the besieged Syrian city of Daraa.
"Recently, there has been a significant increase in the number of Syrians migrating from the shores of Libya across the Mediterranean," it said.
The International Organisation for Migration says that 1,100 people have died on the Central Mediterranean route this year.
Of those intercepted at sea, Sudanese citizens were the largest group, followed by people from Mali, Bangladesh and Egypt.
Although nearly two thirds were men, there were about 1,800 women and 1,300 children, according to the UNHCR figures.
The majority of those rescued were taken back to the Tripoli Naval Base. Others went to a Libyan commercial port or oil refinery.
The UN agency said it had distributed supplies, including nearly 5,000 items of food and more than 600 blankets, to the migrants.
Europe is trying to prevent a new migration crisis at its borders after previous surges triggered a political backlash.
Brussels is supporting a transitional government in Libya, which came to power this year after a decade of chaos. More than 200,000 Libyans are estimated to be displaced in their own country.
Josep Borrell, the EU’s foreign policy chief, said on a visit to Tripoli on Wednesday that Europe could help Libya reform its security sector.
Libya is scheduled to hold an election in December, but ongoing disputes over a legal framework have called this timetable into question.
German Foreign Minister Heiko Maas visited Tripoli on Thursday to open Berlin’s new embassy in the country. Diplomats had left in 2014.