ATHENS — One person is dead and five are missing after a military helicopter operating off a Canadian frigate that was taking part in a NATO operation in the Mediterranean crashed into the sea between Greece and Italy, Canadian Prime Minister Justin Trudeau said. 

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 exercise off the coast of Greece when the incident occurred, according to the Canadian Armed Forces.

Tanya Cowbrough said on Facebook her daughter, Abbigail Cowbrough, had been killed. 

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

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.

"We can confirm that we have contacted all primary family members of those who were on board the helicopter when contact was lost," the Canadian Armed Forces said in a statement. "Search efforts continue with our Allies." 

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.