Initial reports said the helicopter had been 50 nautical miles off the Greek island of Kefalonia, it added.

The helicopter was attached to the Canadian frigate Fredericton from where it had taken off for a patrol.

Italian, Greek and Turkish frigates also took part in the patrol which had moved from Greek to Italian waters on Wednesday, with the Greek frigate remaining in Greek waters.

Greek naval and air forces were ready to assist in a rescue operation "if Italy requests it" a military source told AFP.