ROME/PALERMO: As many as 700 people are feared dead after a boat carrying migrants capsized off the Libyan coast overnight, a United Nations official said on Sunday.

Antonino Irato, a senior official from the Italian border police told television station RaiNews24 that 28 people were rescued in the incident, and 24 bodies had been recovered, adding that the boat had capsized just off Libyan waters, south of the southern Italian island of Lampedusa.

If confirmed, the death toll would bring the total number of dead since the beginning of the year to more than 1,500.

The boat is believed to have capsized when the migrants shifted to one side of the overcrowded vessel as a merchant ship approached.

“The first details came from one of the survivors who spoke English and who said that at least 700 people, if not more, were on board. The boat capsized because people moved to one side when another vessel that they hoped would rescue them approached,” said Carlotta Sami, a spokeswoman for the United Nations High Commissioner for Refugee.

Italian officials said navy and coast guard vessels, as well as merchant ships in the area and a Maltese patrol boat, were involved in the search and rescue operation, which was being coordinated by the Italian coast guard in Rome.

The new deaths fuelled calls for a stronger response from Europe to the increasingly deadly decades-long migrant crisis playing out in the Mediterranean.

International aid groups and Italian authorities have criticised Europe's so-called “Triton” border protection operation, which recently replaced a more comprehensive Italian search-and-rescue mission.

“A tragedy is unfolding in the Mediterranean, and if the EU and the world continue to close their eyes, it will be judged in the harshest terms as it was judged in the past when it closed its eyes to genocides when the comfortable did nothing,” Maltese Prime Minister Joseph Muscat said.

“They are literally trying to find people alive among the dead floating in the water,” he added.

There was still no decision on where the survivors and the bodies that had been recovered would be taken.

Just last week, 400 people were presumed drowned when another boat capsized.

Know more: Nearly 400 migrants die in shipwreck off Libya, 150 rescued

Italian Prime Minister Matteo Renzi said Europe was witnessing “systematic slaughter in the Mediterranean”.

“How can we remain insensible when we're witnessing entire populations dying at a time when modern means of communications allow us to be aware of everything?” Renzi said at a political event in Mantua.