The Canadian military says it has lost contact with one of its helicopters in the Mediterranean.
In a statement, the military says the aircraft from HMCS Fredericton went missing during an exercise off the coast of Greece.
It says a search-and-rescue operation is underway.
NATO spokeswoman Col. Juanita Chang earlier confirmed an incident involving a helicopter from a ship under NATO command.
Chang did not reveal the nationality of the aircraft or vessels.
HMCS Fredericton left Halifax for a six-month deployment around Europe in January with one of the Royal Canadian Air Force's new Cyclones on board.