Migrants rescued by the Libyan coast guard in the Mediterranean Sea arrive at the naval base in the Tripoli on May 6. (Mahmud Turkia/AFP/Getty Images)

Nearly 250 migrants were feared dead in the Mediterranean after two vessels went down in recent days amid a sharp rise in attempts to make the dangerous crossing from Libya to Europe’s southern shores, the U.N. refu­gee agency said Tuesday.

The apparent deaths underscored the huge challenges for European leaders and international groups seeking to cope with rising numbers of refugees and others using Libyan smuggling networks in bids to reach European Union nations.

More than 6,000 migrants have set off on boats into the Mediterranean since late last week, bringing the total this year to more than 43,000, according to the U.N. High Commissioner for Refugees. Another group, the International Organization for Migration, placed the figure at more than 49,000.

Regardless of the total, the count is certain to grow as smuggling operations typically pick up during the warmer months.

Already this year, more than 1,300 people have died at sea after leaving Libya on overcrowded vessels.

Libya has been a gateway for migrant traffic for more than a decade, but the North African coast has become the main route for migrants from Africa and the Middle East after clampdowns along the far shorter sea passage from Turkey to E.U.-member Greece.

In one of the latest incidents in the Mediterranean, a ship went down off the Libyan coast on Sunday, leaving at least 163 people missing and feared dead, the U.N. agency said, citing reports from the International Medical Corps. Seven people were rescued.

Another vessel — an inflatable craft carrying 132 people — sank off the Libyan coast with at least 82 people unaccounted for, the U.N. agency said. About 5o others were rescued and taken to the Sicilian port of Pozzallo.

In February, E.U. leaders agreed to give Libya $216 million to help bolster the fragile nation’s coast guard and navy so that it can stop smugglers’ boats inside territorial waters. Europe also said it would help fund refugee camps in Libya and assist migrants seeking to return to their home nations.