Around 150 migrants heading to Italy drowned when their ship capsized off the Tunisian coast, the International Organization for Migration said in Geneva on Friday.
"The Tunisian Red Crescent confirmed on Thursday that there were still bodies in the water and the recovery operation was ongoing," said the agency in a statement.
"It also said that 150 people, mostly Sub-Saharan Africans, had died and their bodies taken to Sfax Hospital."
The vessel had been packed with refugees, many fleeing the conflict in neighbouring Libya, and was on its way to the Italian island of Lampedusa when it ran aground.
It struck a sandbank some 19 nautical miles (36 kilometres) off the coast of the Italian islands, and then capsized as people struggled to leave the boat to jump into rescue vessels, the TAP news agency reported.
Some 600 people were rescued, but, as of Thursday, up to 270 were missing and rescue workers said there was little hope of finding more survivors.