All eight service members aboard the U.S. military Osprey CV-22 aircraft that crashed into waters off southwestern Japan are believed dead, the Pentagon and White House said Tuesday, making it the aircraft’s deadliest-ever accident.

The crash — the first fatal accident involving an Osprey in Japan — has rekindled concern over the aircraft’s safety, with Japan’s defense chief saying that concerns have yet to be allayed despite a halt in operations of the crashed aircraft’s unit.

U.S. President Joe Biden said Tuesday in Washington that he and his wife were “heartbroken” over the loss of the service members, and that the search-and-rescue operation had ended “after an extensive and weeklong effort” following the Nov. 29 crash in waters off Kagoshima Prefecture’s Yakushima Island.