TOKYO, Dec. 20 (Xinhua) — Japan's top court on Tuesday upheld a lower court's ruling in favor of the central government's plan to relocate a U.S. Marine Corps air base within the island prefecture of Okinawa, despite local people's demands that the U.S. base be relocated outside the prefecture.

According to the top court's ruling, Okinawa Governor Takeshi Onaga acted "illegally" when he revoked in October 2015 an approval issued by his predecessor for the landfill work of the relocation plan.

Onaga has said that he would swiftly retract the revocation, but whether he would explore other options to block the relocation plan has caused attention.

Meanwhile, over 100 people gathered in front of the top court Tuesday afternoon to protest against the ruling, shouting slogans such as "No New Henoko Base."

Japan's central government has been seeking to relocate the U.S. Futenma base from Ginowan to the less populated Henoko coastal area of Nago, saying that it is "the only solution" for removing the dangers posed by the base to the crowded residential area of Ginowan without undermining the Japan-U.S. alliance.

The Okinawa people, however, have called for the base to be removed from the prefecture, complaining of sufferings caused by aircraft noise, crimes committed by the U.S. servicemen as well as safety concerns .

Onaga, well known for his opposition to the plan of relocating Futenma base within the prefecture and elected Governor of Okinawa in 2014, revoked in October 2015 an approval issued by former governor Hirokazu Nakaima for the landfill work of the relocation plan.

The move triggered a legal battle between the central government and the local government last year as the two sides sued each other over the issue, which was halted in March when a settlement deal was reached under court mediation.