Hiroji Yamashiro, a 63-year-old Okinawan and one of the leaders of the protest against an expanded U.S. Marine base on Okinawa, rallies the crowd in front of the gates to the base. (Anna Fifield/The Washington Post)

One of the most vocal opponents of U.S. military construction on Okinawa has been in detention for 95 days on relatively minor charges, triggering accusations that the Japanese government is trying to silence him.

Hiroji Yamashiro, a 64-year-old who had led protests against new U.S. Marine Corps facilities in the island prefecture, was arrested Oct. 17 and has been behind bars ever since.

“I can’t help but think this smells like a political judgment, not a judicial one,” Yamashiro wrote from his prison cell in Naha in response to questions from The Washington Post that were passed to him through his attorney.

“This is an unjust and illegal detention, and I don’t think it should be allowed to happen. It’s probably related to the current situation of the base issue in Okinawa,” he wrote.

Hiroji Yamashiro tells demonstrators to resist peacefully as they protest expansion of a U.S. Marine base at Henoko, Okinawa, on Feb. 1. (Anna Fifield/The Washington Post)

In Japan, suspects can be held for 23 days before legal authorities must either indict or release them. Their attorney is not allowed to attend interrogations conducted during this time.

Yamashiro was arrested on suspicion of cutting a wire fence around a Marine Corps helipad construction site in the forest near Takae in northern Okinawa. Three days later, prosecutors added another charge: interfering with public officers’ duties and causing bodily injury. They alleged that Yamashiro grabbed a civil servant from the Okinawa Defense Bureau and shook him, bruising his arm and hurting his neck, on Aug. 25.

Then, in late November, prosecutors added a third charge: obstruction, accusing Yamashiro of putting concrete blocks on the road in front of the site at Henoko, where a new Marine Corps air station is being built, a full 10 months earlier.

Officials from the Okinawa prefectural police, the Naha local court and the U.S. Marine Corps in Okinawa declined to comment on Yamashiro’s case. But an Okinawa police representative has denied any political motivation.

“The police handled it appropriately in line with specific facts and based on laws and evidence, and we have no intention to put pressure on anti-base protesters,” he said. “We will continue to handle any illegal acts based on evidence and in an appropriate manner.”

The extroverted Yamashiro has long been a thorn in the side of Japanese authorities — and, by extension, American ones — by leading protests against U.S. military construction projects.

This has helped further delay Washington and Tokyo’s plan to close the Marine Corps air station at Futenma, a huge piece of prime land right in the heart of Okinawa’s most densely packed area, and replace it with a new facility next to an existing base in a more isolated area near Henoko.

The latest polls show that more than 80 percent of Okinawans oppose the move. They say that Okinawa bears too much of the burden of Japan’s military alliance with the United States and that the base should be put in another prefecture.

Opponents got a boost in late 2014 when Okinawa elected a governor who vowed to stop the construction. The government’s efforts to put up legal roadblocks and the protesters’ actual roadblocks have complicated and slowed the construction process at Henoko. Forest-clearing for Osprey helipads near Takae has also triggered protests.

The U.S. military has returned some land to Japan, however. Last month, it gave back nearly 10,000 acres in northern Okinawa, the largest transfer since the U.S. occupation of the prefecture ended in 1972.

Even in this tense climate, Yamashiro’s lengthy detention was “especially abnormal,” said Shunji Miyake, one of Yamashiro’s attorneys. They have requested bail several times, but it has been repeatedly denied. Yamashiro, who underwent cancer treatment in 2015, has not been allowed to see his family since his arrest in October.

“None of the charges are serious enough to detain him for this long. I suspect that this is to keep him away from the protest ground,” Miyake said.

Yamashiro’s supporters this week gave the court a petition with 40,000 signatures, calling for his release.

Lawrence Repeta, an American attorney who teaches law at Meiji University in Tokyo, said the U.S. government should be concerned about Yamashiro’s treatment.

He said Yamashiro’s continued incarceration contravenes the International Covenant on Civil and Political Rights, which Japan ratified in 1979. That document states that it “shall not be the general rule that persons awaiting trial shall be detained in custody.”

“It seems obvious that this is a political arrest for political reasons,” Repeta said. He called all three of the charges “trivial.”

“It appears that he is simply being punished,” Repeta said. “The U.S. government should be asking what’s going on here. Locking up a sick old man will only strengthen Okinawans’ resolve to fight.”

Yamashiro, for one, is not dissuaded. “I will not get discouraged,” he wrote. “I will survive through this and work hard to speak for angry Okinawan people.”

Yuki Oda contributed to this report.