A United States Navy aircraft with 11 crew members and passengers on board crashed into the ocean southeast of Okinawa, Japan, on Wednesday, the U.S. Seventh Fleet said in a statement.

The aircraft was headed to the USS Ronald Reagan aircraft carrier, which is deployed to the Philippine Sea. A search and rescue operation was launched from the carrier, the Seventh Fleet said. It said later that a search was still underway for three missing personnel, and that eight had been rescued in good condition.

Japanese Minister of Defence Itsunori Onodera told reporters that U.S. Navy officials had informed him the crash could be the result of engine problems. The U.S. Navy said earlier that the cause of the crash was unclear.

Eight of the people on board were found, Japan’s defense minister told reporters, but it was unclear whether they were alive. The Defense Ministry said it had no information on their condition.

The C-2 “Greyhound” aircraft crashed into the Pacific about 90 miles northwest of Okinotorishima, a Japanese atoll, Onodera said, according to a ministry spokesman.

The names of the crew and passengers were being withheld pending notification of next of kin.