A boat with at least 700 migrants on board has capsized off the Greek island of Crete.
The International Organization for Migration (IOM) said more than 340 had been rescued with hundreds more still missing on June 3.
Four bodies have been recovered, according to Greek authorities.
In a statement, the IOM said any confirmed deaths "would be the first fatalities in Greek waters since April."
A controversial deal in March between the EU and Turkey led to a sharp drop in the flow of migrants to Greece.
More than 205,000 migrants and refugees have crossed the Mediterranean to Europe so far this year.
Three-quarters of them, mainly refugees fleeing conflicts in Syria and Afghanistan, arrived in Greece before the end of March, with 376 dying trying to make the perilous journey, according to IOM figures.