The International Organization for Migration (IOM) said today that a tragedy in which as many as 500 migrants may have drowned last week was "the worst shipwreck in years" and a case of mass murder.

"If this story, which police are investigating, is true, it would be the worst shipwreck in years... not an accident but a mass murder, perpetrated by criminals without scruples or any respect for human life," IOM said in a statement.

According to the survivors, the boat set out from Damietta in Egypt on September 6, and the migrants were forced to change boats several times during the crossing towards Europe.

At one time the traffickers, who were on a separate boat, ordered the migrants to transfer onto a smaller vessel. The migrants feared it was too small to hold them and refused. The furious traffickers then rammed their boat until it capsized.

"Two survivors brought to Sicily told us that there had been at least 500 people on board.

Nine other survivors were rescued by Greek and Maltese ships, but all the rest appear to have perished," Flavio Di Giacomo, IOM's spokesman in Italy, told Agence France-Presse.

The alarm was raised when a freighter rescued two Palestinians from the sea some 300 miles south east of Malta. They said they had been in the water for a day and a half.

Cargo ships and units of the Italian Navy subsequently picked up a small number of migrants, including three who were brought to Malta.