Around 60 migrants drowned after the rubber dinghy they were travelling in capsized in the Mediterranean, survivors told the International Organisation for Migration when they arrived in Italy, the IOM said on Friday.
Eighty survivors were rescued and brought to the southern Italian port of Brindisi, where they said that their boat originally carried around 140 people, IOM spokesman Flavio Di Giacomo said on Twitter.
Di Giacomo tweeted that the dinghy had gone down this week but did not specify on which day. It was not immediately possible to reach him directly.
Italy is the main point of arrival for mostly African migrants to European shores this year, with boats sent out almost daily from lawless Libya.
About 10,000 people have been rescued from flimsy vessels over the past three days, and Italy has taken in 82,000 people so far this year.
On Thursday, the European Commission threw its weight behind a plea by Italy for fellow EU states to allow rescue boats carrying African migrants to dock in their ports to alleviate growing pressure on Rome.