A dolphin jumps in front of a raft overcrowded by Syrian refugees while crossing a part of the Aegean Sea from Turkey (seen in the background) to the Greek island of Lesbos on Oct. 21, 2015. REUTERS/Yannis Behrakis

Three Greek naval airmen were missing and feared dead after a Greek navy helicopter crashed early on Thursday off the small island of Kinaros in the eastern Aegean Sea, Greece's Defence Ministry said.

"The Agusta Bell helicopter was taking part in the night military exercise 'Τhunder'. It had taken off from a frigate sailing in the area and disappeared from radar around 0045 GMT. Wreckage has been found near Kinaros," a ministry official said.

Kinaros is an islet near the island of Amorgos.

Armed forces chief Vangelis Apostolakis said weather conditions had been normal at the time when radar contact and communications were lost.

He said only parts of the wreckage had been found, and that there was little hope that any of the crew would be found alive.

Turkey issued a Notice to Airmen saying the Greek rescue operation was within its maritime search and rescue region and that all efforts should be coordinated with Turkish authorities.