In 2012, the United States said it would redeploy 9,000 Marines from the island where communities complain bases are an unfair burden -- with objections ranging from pollution to noise and helicopter crashes.

The relocation began with "a small detachment of approximately 100 logistics support Marines" transferred to the US island territory of Guam, Japan's defence ministry and the US Marine Corps said.

"Commencement of relocation to Guam signifies the first phase of relocating Marines to locations outside of Japan," said the joint statement.

There are currently around 19,000 Marines in Okinawa -- strategically located east of Taiwan, which has become a flashpoint for tensions between the United States and China.

Beijing claims Taiwan as part of its territory and has not ruled out the use of force to bring the self-ruled island under its control.

Washington is Taiwan's most important backer and biggest supplier of arms, but has long maintained "strategic ambiguity" about the prospect of backing it with boots on the ground.

The 9,000 relocating Marines are set to be moved elsewhere in the Pacific -- to Guam, Hawaii or Australia, the United States has said.

Okinawa comprises just 0.6 percent of Japan's territory but hosts more than half of the 50,000 US troops posted in the country.

The 1995 gang rape of a 12-year-old girl by three US soldiers in Okinawa also prompted widespread backlash, with calls for a rethink of the 1960 pact allowing the United States to post soldiers in Japan.