The death toll from a ship carrying 86 migrants which capsized last week off the coast of Tunisia has risen to 58, the Tunisian Red Crescent said on Thursday.

"Only today, the Coast Guard recovered 38 bodies off the coast of Zarzis, bringing the death toll to 58," Mongi Slim, an official of the Tunisian Red Crescent, told Reuters.

The United Nation's refugee agency (UNHCR) said last week that more than 80 people were feared drowned after the boat capsized in the night of July 3.

Passing Tunisian fishermen had only been able to rescue four people but one of them passed away after being brought back to shore.

Survivors told the Tunisian coast guard that the boat had set off from Libya.

The Tunisian Red Crescent believes that the eventual toll from the incident could be higher than 80, which would make it one of the worst migrant boat disasters to date.

READ MORE: Boat carrying 70 migrants capsizes off Tunisian coast