A humanitarian rescue ship on Tuesday found 13 dead bodies on a rubber boat off the coast of Libya that was carrying more than 160 migrants, charity group Proactiva Open Arms said.

"Several pregnant women and mothers among the (dead)," Proactiva's founder Oscar Camps wrote on Twitter.

A spokesman for Italy's coastguard said some 260 migrants had been rescued from different boats on Tuesday. Some 600 people were rescued from the southern Mediterranean yesterday.