TORONTO (AP) — One person is dead and five are missing after a military helicopter operating off a Canadian frigate during a NATO exercise crashed into the sea between Greece and Italy, Canadian Prime Minister Justin Trudeau said Thursday.

Trudeau said one body was found, and the five others aboard the aircraft are missing.

“We hold out hope to find the missing,” Trudeau said.

The Cyclone helicopter was deployed on board the Halifax-class frigate HMCS Fredericton and was participating in a NATO training exercise off the coast of Greece when the incident occurred, according to the Canadian Armed Forces.

Gen. Jonathan Vance, Canada’s top military official, said the ship lost contact with the aircrew on Wednesday evening and that flares were spotted from the water minutes later. Vance said flares would have been automatic when it ditched.

He confirmed the body of Abbigail Cowbrough has been recovered. She was 23.

Tanya Cowbrough said on Facebook her daughter had been killed.

“My beautiful daughter has been in a military accident and passed away," she wrote. “Nothing can replace her.”

Shane Cowbrough said he lost his oldest daughter.

"I am broken and gutted," he posted. “There are no words. You made me forever proud. I will love you always, and miss you in every moment.”

Canadian Defense Minister Harjat Sajjan said they have recovered the flight data recorder but said the cause of the accident remains unknown at this time. Multiple NATO countries are in an ongoing search-and-rescue operation in the Ionian Sea, hoping to find the five others.

Vance said the voice and data recorders floated away from the wreckage. A beacon allowed them to find it.

He said they have placed Canada's Cyclone helicopter fleet on “operational pause."

“We have to rule out that there is a fleet-wide problem,” he said.

The Royal Canadian Air Force’s Cyclone helicopters carry a crew of four, including two pilots, a tactical operator and a sensor operator with space for several passengers. They are primarily based on naval vessels and used for hunting submarines, surveillance and search and rescue.

The Canadian military only started using them on missions in late 2018 after more than a decade of developmental challenges, delays and cost overruns. The crash is also likely to raise questions about the aircraft.

The military was originally supposed to have received 28 Cyclones from manufacturer Sikorsky starting in November 2008. But the first helicopter wasn’t delivered until June 2015 and even then, they were missing vital equipment and software and only suitable for training.

Lockheed Martin, which owns Sikorsky, said in a statement that Sikorsky is sending an investigator to assist at the request of the Canadian military.