Chief Cabinet Secretary Hirokazu Matsuno, the government’s top spokesperson, said Friday that Japan was “concerned that Osprey flights have been conducted despite repeated requests from the Japanese government and without sufficient explanation regarding the confirmation of their flight safety.”

The Pentagon said Thursday it had not received any official request.

“Right now, the Ospreys are still operating in Japan,” spokesperson Sabrina Singh said at a news briefing, adding that the focus was on search and rescue efforts.

Matsuno said Friday that the United States had told Japan that while it had suspended operation of CV-22 Ospreys like the one that crashed, other models were being operated “after thorough and careful maintenance and safety inspections.”

“We will continue to urge the U.S. side to confirm the safety of the flight before conducting these flights,” Matsuno said.

The U.S. Embassy in Japan did not immediately reply to a request for comment on Friday.

Use of the American-made Ospreys in Japan, a key U.S. ally and the first foreign country to own and operate the aircraft, has been a contentious issue amid questions about its safety.

The hybrid aircraft takes off, lands and hovers like a helicopter but can fly like a fixed-wing plane.

Ospreys have been involved in a number of accidents since they were introduced in 2007. In August, an Osprey with 23 U.S. Marines on board crashed in Australia during a routine training exercise, killing the pilot and two others.

Arata Yamamoto reported from Tokyo, and Mithil Aggarwal reported from Hong Kong.