TOKYO (AP) — Japan's top government spokesperson expressed concern Friday that the U.S. military is continuing to fly Osprey aircraft in the country without providing adequate information about Wednesday's fatal crash.

One crew member was killed and seven others are missing following the crash off southern Japan, the Air Force Special Operations Command said in a statement Friday. One set of remains has been recovered, the Air Force said.

The search for the aircraft and missing crew members continues, the command said.

“Search and rescue operations consist of a combination of air, surface, and subsurface search of water and coastline in the vicinity of Yakushima, Japan, in order to locate the crewmembers,” the command said.

The cause of Wednesday's crash, which occurred during a training mission, is still under investigation. Search operations widened Friday with additional U.S. military personnel joining the effort, while Japanese coast guard and military ships focused on an undersea search using sonar.

The Pentagon said Thursday that U.S. Ospreys continue to operate in Japan, and Deputy Press Secretary Sabrina Singh said she was not aware of an official request from Japan to ground them.

“We are concerned about the continuing Osprey flights despite our repeated requests and the absence of a sufficient explanation about their safety from the U.S. military, Chief Cabinet Secretary Hirokazu Matsuno said Friday.

In a statement Friday, Singh clarified that while U.S. Osprey operations continue in Japan, the remaining five Ospreys from the squadron involved in Wednesday's crash are not flying at present. Air Force Special Operations Command makes up just a small number of the Ospreys assigned to Japan, most are operated by the U.S. Marine Corps.

Singh said the Pentagon has been communicating with the Japanese government on the crash.

We have already started sharing information about the accident with our Japanese partners and have pledged to continue to do so in a timely and transparent manner,” Singh said.

The U.S.-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 airplane, during flight.

Ospreys have had a number of crashes, including in Japan, where they are used at U.S. and Japanese military bases, and the latest crash rekindled safety concerns.

Japanese officials say they asked the U.S. military to halt Osprey flights in Japan except for those involved in the search operations.

Defense Minister Minoru Kihara said he met with the commander of U.S. Forces Japan, Lt. Gen. Ricky Rupp, on Thursday afternoon and repeated his request that flights be allowed only after the aircraft's safety is confirmed. He acknowledged that he did not specifically use the words “grounding” or “suspension.”

Kihara said he asked Rupp to explain what measures are being taken for Osprey flights in Japan in response to the crash.

He said the U.S. told his ministry that while the five CV-22 Ospreys deployed with the one that crashed are currently not in use, others deployed on Okinawa are being operated after thorough safety checks, and that it will provide as much information and transparency as possible.

On Thursday, Japanese Foreign Minister Yoko Kamikawa met with U.S. Ambassador to Japan Rahm Emanuel and asked the United States “to promptly provide information to the Japanese side.”

The CV-22B Osprey that crashed was one of six deployed at Yokota Air Base, home to U.S. Forces Japan and the Fifth Air Force, and was assigned to the 353rd Special Operations Wing.

The aircraft had departed from the U.S. Marine Corps Air Station Iwakuni in Yamaguchi prefecture and crashed on its way to Kadena Air Base on Okinawa, Japanese officials said.

A total of 44 Ospreys have been deployed at U.S. and Japanese military bases in Japan. In Okinawa, where about half of the 50,000 American troops in Japan are based, Gov. Denny Tamaki called on Japan’s defense and foreign ministries to request the U.S. military to suspend all Osprey flights in Japan, including in search operations.

“It is extremely regrettable that Ospreys are still flying in Okinawa, Tamaki said in a statement Thursday. “I have serious doubts about Osprey safety even for their search and rescue operations.”

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Tara Copp contributed to this story from Washington.