But coming just as Washington and Tokyo were finalizing plans to send the first Ospreys to Okinawa -- where the U.S. military footprint is always a sensitive political issue -- the accidents could not have happened at a worse time.

In hopes of easing longstanding complaints that Okinawa bears too much of the burden of hosting the U.S. troops in Japan, the two governments in April announced that about 9,000 of the nearly 20,000 Marines there will be moved elsewhere.

Crowding around U.S. bases on Okinawa is particularly intense, and opponents of the bases often complain of the danger of accidents involving local residents, noise from training and base-related crime.

The dispute over the Ospreys has renewed those complaints.

"If the two governments force the deployment of these aircraft on Okinawa as scheduled, there will be an explosion of anger," Kantoku Teraya, a national lawmaker from Okinawa, told reporters Wednesday after submitting a petition to Prime Minister Yoshihiko Noda calling for the deployment to be scrapped.