At least 70 migrants are believed to have drowned when their boat capsized in the Mediterranean Sea, 40 miles off the Tunisian coast.
The vessel is believed to have left neighbouring Libya on Thursday where renewed fighting between rival factions has gripped the capital Tripoli.
Sixteen survivors were rescued by the Tunisian navy and taken to the port of Zarzis.
It is believed to be one the deadliest shipwrecks involving migrants trying to reach Europe this year.
“This is a tragic and terrible reminder of the risks still faced by those who attempt to cross the Mediterranean,” UNHCR Special Envoy for the Mediterranean Vincent Cochetel said.
In the first four months of 2019, 164 people are known to have died on the route, with one fatality for every three who reach European shores.
Earlier on Friday, UNHCR spokesman Babar Baloch said the UN had repeatedly voiced its concerns about the lack of boats to pick up migrants and refugees fleeing from “the horrendous and horrible situation” in Libya.
It was not immediately known which countries the migrants involved in Friday’s tragedy were from.
According to UN agency the International Organisation for Migration (IOM), 2,297 migrants died or went missing in the Mediterranean last year out of a total of 116,959 people who reached Europe by sea.