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An Afghan man jumps off an overcrowded raft onto a beach at the Greek island of Lesbos in OctoberYannis Behrakis/Reuters

As many as 500 people are feared dead after a boat transfer in the Mediterranean turned deadly, the UN refugee agency announced on 20 April. The incident occurred when smugglers attempted to move them from smaller boats to a larger vessel between Libya and Italy.

The UN said the incident was reported by 41 survivors, who were part of a group of between 100 and 200 people who left near Tobruk, Libya on a boat some 30-metres long. "After several hours at sea, the smugglers in charge of the boat attempted to transfer the passengers to a larger ship carrying hundreds of people in terribly overcrowded conditions," the UNHCR said. "At one point during the transfer, the larger boat capsized and sank."

The agency said survivors, which included those who had not boarded the larger vessel yet and those who managed to swim back to the smaller boat, drifted in the sea for possibly three days before they were rescued. The rescued people include 23 Somalis, 11 Ethiopians, six Egyptians and a Sudanese person. They were rescued by a merchant ship and taken to Kalamata, in the Peloponnese peninsula of Greece.

The International Organisation for Migration (IOM) said survivors described the incident that may have "caused the death of upwards of 400 migrants and refugees." Survivors told both the UNHCR and the IOM that the larger boat was overcrowded and soon began to take on water before it capsized and sank.

"I saw my wife and my two-month old child die at sea, together with my brother-in-law," a survivor identified as Mohamed told the IOM. "The boat was going down...down...all the people died in a matter of minutes. After the shipwreck we were drifted at sea for a few days, without food, without anything, I [thought] I was going to die."

The shipwreck comes nearly a year after more than 800 migrants drowned as their overcrowded ship capsized between Libya and Italy. Only 28 people survived the incident which is still remembered as the worst maritime disaster ever recorded in the Mediterranean.

The reports by UNHCR and the IOM clarify rumours that circulated regarding the shipwreck. Conflicting reports claimed the ship had left from Egypt or that survivors had been taken to Italy or Greece, The Guardian reported.

On 18 April, the Italian coastguard told IBTimes UK that they had no information on the incident and had not received distress calls. "We have learned about this from the press," a coastguard spokesman said. The spokesman added that no related search and rescue operation was underway.

In a separate incident off the coast of Libya, the Italian coastguard said 108 people were rescued from a semi-submerged rubber-dinghy that had encountered rough seas. Survivors said the dinghy's engine had broken and part of the boat had taken on water. Forty-two people were swept away by the waves and are believed to have died, while another two died when jumping into the waters as humanitarian group SOS Mediterranee conducted a rescue mission.

The UNHCR reports that 179,552 refugees and migrants have reached Europe by crossing the Mediterranean or Aegean seas. At least 761 have died or gone missing during the treacherous crossing.