Recent crashes involving the U.S. military's latest transport aircraft are fueling an uproar in Japan that could threaten plans to deploy them to the southern island of Okinawa by the end of the year.

Following an uproar on Okinawa and in another city likely to host the Osprey aircraft, U.S. officials were to brief Japanese government representatives in Washington on Friday.

The Osprey craft can fly like a helicopter or an airplane and has been used in combat in Afghanistan and Iraq. But a crash in April killed two Marines and another last week injured five airmen.

Japan's top government spokesman said last week the plan to deploy the aircraft to Japan this year couldn't move forward until Tokyo received assurances of its safety.

While saying the U.S. takes Japan's concerns seriously, a Pentagon spokesman on Thursday said the U.S. stands by the aircraft.

"The Osprey is a highly capable aircraft with an excellent operational safety record," Pentagon press secretary George Little said.