The International Organization for Migration said Monday it had received a distress call from a sinking boat in the Mediterranean carrying more than 300 people, with at least 20 people reported dead.

IOM's Rome office has received a call for help from one of three boats floating near each other in international waters, spokesman Joel Millman said.

"The caller said that there are over 300 people on his boat and it is already sinking (and) he has already reported fatalities, 20 at least," he wrote in an email.