Japan has suspended flights by its Osprey aircraft after a US Air Force Osprey based in Japan crashed into the sea during a training mission. Tokyo on Thursday said it also asked the US military to ground all Ospreys operating in Japan except for those joining the search operations at the crash site. At least one of the eight crew members aboard was killed in the crash, but the status of the others was not yet known. The Pentagon said US Ospreys continue to operate out of Japan. The deputy press secretary, Sabrina Singh, said she was not aware of an official request from Japan to freeze Osprey flights. A senior defence ministry official, Taro Yamato, told a parliamentary hearing that Japan has suspended flights of Ospreys until details of the crash and safety are confirmed. The cause of Wednesday's crash was not yet known. The US-made Osprey is a hybrid aircraft that takes off and lands like a helicopter but can rotate its propellers forward and cruise much faster, like an aeroplane, during flight. Ministry officials said a planned training flight Thursday at the Metabaru army camp in the Saga prefecture in southern Japan was cancelled as part of the grounding of all 14 Japanese-owned Ospreys deployed at Japan's Ground Self-Defence Force bases. Defence officials said they hoped the US side got the message, but NHK national television said a number of Ospreys flew in and out of a US air base on Okinawa. One US Osprey has joined the rescue operation off Japan's southern coast, defence officials said. A US defence official said if there was a pause in flights, it could also be to allow the small Air Force Special Operations Command community in Japan time to process its unit's crash, the official said. The official spoke on the condition of anonymity to discuss sensitive details about the crash. The coast guard, as well as Japanese troops, searched through the night, and on Thursday the coast guard started using sonar to search underwater for the broken aircraft, which might have sunk to the sea bottom, at a depth of about 30m. On Thursday, Japanese Foreign Minister Yoko Kamikawa met with US Ambassador to Japan Rahm Emanuel at her ministry, asking the United States "to promptly provide information to the Japanese side". Emanuel said the focus now is the search for the missing crew members and he thanked Japanese troops, coast guard and local fishermen for "being side by side". US Air Force Special Operations Command said the CV-22B Osprey was one of six deployed to Yokota Air Base, home to US Forces Japan and the Fifth Air Force, and assigned to the 353rd Special Operations Wing.