TOKYO - Two US servicemen were arrested in Japan's southern island of Okinawa on suspicion of raping a Japanese woman, police said on Wednesday, in an incident that could strain Tokyo's ties with its closest ally Washington.

The case comes at a time when public opinion in Okinawa is at odds with Tokyo for allowing the US deployment of Osprey hybrid aircraft on the island despite lingering concerns about their safety.

The arrests also coincide with a sharp deterioration in Japan's relations with China over a disputed East China Sea island chain that makes it strategically important for Tokyo to reaffirm its alliance with the United States.

US ambassador to Japan John Roos said in a statement that his government was extremely concerned by the incident and was committed to cooperating fully with the Japanese authorities in their investigation.

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