Two U.S. Air Force Osprey aircraft made emergency landings Monday afternoon at the airport on Amami-Oshima island in Kagoshima Prefecture, local authorities said.
The U.S. military said a warning light came on in one of the Ospreys, and Defense Minister Itsunori Onodera said he heard "one of the two Ospreys seems to have had a problem."
The two were among five CV-22 Ospreys that arrived at Yokota Air Base in suburban Tokyo in April ahead of their deployment there this summer.
All five Ospreys left Yokota in the morning and were on their way to Kadena Air Base in Okinawa. Three arrived there in the afternoon.
Two Ospreys landed at Amami Airport at around 3 p.m., and local authorities said there were no reports of casualties or obvious damage to the tilt-rotor aircraft. One of them departed at around 5:40 p.m.
The emergency landings may add to safety concerns in Japan over the U.S. military's Osprey aircraft, which has a record of accidents and mishaps in and outside the country.
While a Marine Corps variant of the Osprey, the MV-22, is already stationed in Okinawa, the deployment of the CV-22 at Yokota will be the first time the aircraft is assigned to a base in mainland Japan.