Supporters of a prominent opponent of U.S. military bases in Okinawa held a rally Thursday outside the Japanese Consulate in New York calling for his release from more than four months’ detention.

The move came after Japan’s Supreme Court last month denied bail to Hiroji Yamashiro, head of the Okinawa Peace Action Center. Human rights and civic groups are calling for him to be released from what they say is political oppression.

“I suspect the detention is to crush nonviolent (peace) movements in Okinawa. It is a flagrant violation of human rights,” said Noriko Oyama, who led the rally in front of the Japanese Consulate General.

Yamashiro, 64, has led protest groups against the long-opposed bilateral plan to move U.S. Marine Corps Air Station Futenma from Ginowan to Nago in Okinawa.

He was arrested in October on suspicion of cutting barbed wire near a U.S. construction site in Higashi, where a helipad was being built. He has also been charged with injuring a Defense Ministry official and obstructing relocation work at another U.S. Marine base in Nago. The nature and seriousness of the injury was not clear.

Amnesty International Japan has called for Yamashiro’s immediate release, saying he does not meet the criteria for being detained because the chances of him destroying evidence concerning his alleged crimes are very low.