Japanese demonstrators have staged a rally in the country’s southernmost prefecture of Okinawa to express their outrage over a controversial plan to relocate a US military base there.

On Sunday, the protesters chanted anti-US slogans and carried placards reading, “No new base.”

They also called for the closure of the Marine Corps Air Station Futenma and demanded that American troops be moved completely off the island.

Meanwhile, thousands of people gathered Sunday outside the National Diet, Japan's bicameral legislature, in the capital, Tokyo, to protest the plan to relocate the US military base.

Various speakers described as harmful the presence of US forces in Okinawa, pointing to the deployment of excessive force to contain anti-base protests and environmental damage.

Catherine Jane Fisher, a speaker addressing the demonstrators, argued that if terrorism is “violence against civilians for political goals” then “we have terrorists in Okinawa.”

The United States plans to move the Marines Corps' Futenma air base to a more remote coastal area called Henoko in Nago City to consolidate its troop presence in Okinawa.

Washington and Tokyo first agreed in 1996 to relocate the base from a more congested part of Okinawa to Nago, but opposition from local people and environmental groups has prevented construction in the small town of nearly 60,000 people.

About half of US forces in Japan are based in Okinawa. Many locals have complained about base-related crimes, noise and the risk of accidents.

Susumu Inamine, the mayor of Nago, had earlier issued a statement protesting the move.

"Pushing forward with this tramples on the human rights of the people, and the rich diverse natural life of this region. This is no longer about democracy," Inamine said.

The latest protest rally also comes amid the high number of sexual assaults by US military personnel in Japan, as many offending soldiers receive either no or very light punishments.

According to documents obtained by the Associated Press, American military personnel were involved in more than 1,000 sex crimes between 2005 and 2013 in Japan.

MP/HMV/SS