Aid group Doctors Without Borders (MSF) says 25 migrant men and women have been found dead at the bottom of a rubber boat in the Mediterranean, and 107 survivors were rescued from the same raft.
The bodies were discovered late on Tuesday (local time), an MSF spokeswoman said.
MSF's Mediterranean rescue unit said on Twitter: "23 of the rescued people had horrific chemical burns, seven were so severely injured that they needed to be evacuated to Italy, two by helicopter".
More than 3500 people have died or disappeared trying to cross the Mediterranean from North Africa this year, the International Organization for Migration estimates.
Rescuers plucked 500 migrants from overcrowded boats to safety on Tuesday, Italy's coast guard said.