The U.S. Marines conducted their first test flights of the MV-22 Osprey aircraft in Japan on Friday after months of protests over safety concerns.

The hybrid aircraft can take off like a helicopter and fly like an airplane. Flight operations were conducted at a base in southern Japan where they are temporarily deployed before being transferred to Okinawa.

Protesters held up signs opposing the deployment while the test flights were under way.

Following two recent crashes, tens of thousands of Okinawans have protested the deployment, saying that they are not safe to fly in Okinawa's crowded environment.

But Japan's central government gave the green light for operations to begin this week after a visit by U.S. Defense Secretary Leon Panetta, who said Washington is confident in the safety of the aircraft. The planes are to head to Okinawa this month.

Japanese media reported that a man who defaced a monument at the Hiroshima Memorial Peace Park claimed he did so because he was upset over the Osprey deployment. The reports said the man had been drunk and was arrested on suspicion of vandalism.

Calls to Hiroshima police were not answered late Friday. The red paint that was sprayed onto the cenotaph for victims of the 1945 atomic bombing has been removed.