TOKYO (REUTERS) - A US military helicopter crashed on Japan's southern island of Okinawa on Monday, public broadcaster NHK and police said, an incident that could add to anger over the concentration of US military bases on the island.

NHK said the crash occurred in a mountainous area near a US Marine base in central Okinawa, and video footage showed smoke rising from a fire on what appeared to be a remote moutainside.

Casualties were not known. A spokesperson for the US military in Japan could not immediately comment on the report.

Fire and police officials also could not comment.