A U.S. military helicopter made a forced landing Tuesday night on a tiny island in Okinawa, local police said, making it the third such incident in the island prefecture in less than a month.

The AH-1 attack helicopter made what the U.S. military called a precautionary landing at 8 p.m. at a heliport operated by Tonaki village, west of Okinawa's main island. The two crew members aboard the helicopter were not injured, according to the police.

A malfunction in the hydraulic system was detected, they said.

According to Japanese government sources, the U.S. military has told the Japanese government a warning light came on and led to the landing of the AH-1, which belongs to U.S. Marine Corps Air Station Futenma in Okinawa.

The U.S. military also told Japan it will send mechanics to the island Wednesday. If no problems are found in the aircraft, the helicopter is expected to head back to Futenma, the sources said.

The incident is likely to further fuel safety concerns, as Japan's central and local governments have recently been questioning the frequency of accidents involving U.S. military aircraft in Okinawa, which hosts the bulk of U.S. forces in Japan.

"We're lost for words. Simmering anger among the people in the prefecture could explode," a senior Okinawa government official told reporters.

Two forced landings occurred earlier in the month. In one of the cases, an AH-1 made a precautionary landing at a waste disposal site in the village of Yomitan.

In December, a window fell from a CH-53E large transport helicopter as it was flying over an elementary school just outside the Futenma base.

No one was injured in the three incidents.

Tonaki Island is located about 58 kilometers northwest of Okinawa's capital Naha. The population of the village was 378 as of the end of December.

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