The coastguard on Thursday retrieved the bodies of 20 migrants from sub-Saharan Africa from waters off Tunisia after their boat capsized, a spokesman for the Tunisian defence ministry said.
Five other migrants who were on board were rescued, ministry spokesman Mohamed Zekri told AFP, adding that a search operation is still underway.
Zekri did not give further details but said the rescue operation took place off Sfax in central Tunisia.
But Khaled Hayouni, a spokesman for the interior ministry, gave a different number of confirmed dead, saying 15 bodies had been retrieved.
He said the boat was heading to Italy from the Sidi Mansour district of Sfax.
Tunisia is just a few hundred kilometres from mainland Europe and has long been a launchpad for illegal migration to the continent.
Departures by desperate migrants seeking a new life in Europe peaked in 2011 following the revolution that overthrew Tunisian dictator Zine El Abidine Ben Ali.
Although numbers have dropped significantly in recent years, illegal crossings from Tunisia to Europe jumped by more than 150 percent in January to April compared to the same period last year, according to the UN refugee agency.
Most of the migrants are from sub-Saharan African countries fleeing economic hardship and crisis at home.
According to the interior ministry, 8,581 migrants were intercepted after setting off on the perilous Mediterranean crossing between January and mid-September.
Of those, 2,014 were non-Tunisians.
Earlier this month, the Tunisian navy said it had intercepted 93 African migrants after their boat broke down off Sfax during an attempt to reach Italy.