Dec. 3 marks the 500th day Jason Rezaian has been imprisoned in Iran. The Washington Post strongly denies any wrongdoing by Rezaian and calls his detention “cruel and arbitrary.” (The Washington Post)

The Washington Post and other supporters of journalist Jason Rezaian on Wednesday amplified demands for his release from Iranian custody, a day before the reporter marks 500 days since his arrest and subsequent closed-door trial on charges that included espionage.

The new pressures, including updated filings by The Post with a U.N. panel, seek to boost international leverage on Iran after the reported conviction and sentencing of Rezaian, The Post’s correspondent in Tehran.

The case has drawn widespread outrage from media-freedom groups and sharp criticism from senior Obama administration officials and U.S. lawmakers.

The Post, meanwhile, has strongly denied any wrongdoing by Rezaian and has called the detention “cruel and arbitrary” treatment of a journalist who never strayed beyond the normal work of news gathering.

“This isn’t a real case,” said David W. Bowker, an attorney at the firm of WilmerHale who is representing The Post, “but rather a case of political theater.”

Jason Rezaian’s journey has taken him from a childhood in San Francisco to his father’s native Iran. At 37, he became the Washington Post correspondent in Tehran. In July 2014, he was thrown into Iran’s Evin Prison, where he remains. This is his story. (Jorge Ribas/The Washington Post)

Iran, however, has not publicly clarified the allegations against Rezaian during sessions in Tehran’s Revolutionary Court, which barred his family and others from attending. Last month, Iranian state media reported that Rezaian — a dual Iranian American citizen — had been sentenced to a prison term after his apparent conviction in October but gave no other details.

Martin Baron, executive editor of The Post, called the 500-day mark in Rezaian’s detention “the grimmest” of milestones — 56 days longer than the hostages held at the U.S. Embassy in Tehran after the 1979 Islamic revolution.

“Five hundred days robbed of his life, 500 days deprived of his family, 500 days denied any semblance of justice,” Baron said in a statement.

“Jason has done nothing wrong,” he added. “Iran has never even bothered to produce any evidence against him. His so-called trial was a sham. Recent announcements, without details, of his supposed ‘conviction’ and ‘sentencing’ have only added new layers of cruelty.”

The Post has filed a supplementary petition with the U.N. Working Group on Arbitrary Detention, expanding on a July filing calling for Rezaian’s immediate release and appealing to the world body to intervene.

The new documents, made public by The Post on Wednesday, list an array of concerns including the deteriorating heath of the 39-year-old Rezaian, who suffers from high blood pressure and other ailments as “Iran’s mistreatment of him has intensified.”

The filing further outlines many failings in Rezaian’s trial, including lack of openness on the charges, barring Rezaian’s lawyer from examining evidence and witnesses, and the murky outcome of “farcical legal proceedings.” Rezaian’s attorney, Leila Ahsan, is prohibited from discussing the case with media outside Iran.

The Post’s supplementary documents, filed with the United Nations on Nov. 25, also touch on speculation that Rezaian has become caught in a power struggle between Iranian hard-liners controlling the judiciary and reform-minded opponents including the government of President Hassan Rouhani.

Such battles have flared for years on a range of disputes — most recently over the nuclear deal between Iran and world powers including the United States.

There has been no clear declaration of an internal feud over Rezaian. But Iranian media on both sides have published contrasting narratives on the Rezaian case, including whether Iran is possibly seeking a swap of Rezaian for Iranians held in U.S. custody.

Post attorney Bowker said he expects an advisory opinion from the U.N. group that could increase calls for Rezaian’s release.

“Iran needs to hear the world’s outrage,” said Douglas Jehl, the foreign editor at The Post.

On Thursday, Rezaian’s brother, Ali, plans to deliver a petition to Iran’s permanent mission to the United Nations containing more than 500,000 signatures calling for Rezaian’s “immediate and unconditional release.”

He said additional initiatives are needed in tandem with possible diplomatic appeals by Washington, which does not have official relations with Iran but works through Switzerland and other intermediaries.

“It’s very frustrating that he remains in jail,” said Ali Rezaian. “Whatever anyone is doing or trying to do, it isn’t working.”

Rezaian was arrested July 22, 2014, along with his wife, Yeganeh Salehi, and two photojournalists. All but Rezaian were eventually released on bail. Salehi, an Iranian, is a correspondent for The National newspaper based in Abu Dhabi. It remains unclear whether Iran will seek to bring the others to trial.

Three other American citizens are known to be held by Iran.

Saeed Abedini, a Christian pastor, has been in Iranian custody since September 2012. He was convicted of security-related charges that include claims of proselytizing.

Amir Hekmati, a former U.S. Marine, was detained in August 2011 while on a family visit to Iran. He was convicted in early 2012 on espionage and other charges. A death sentence was reduced to 10 years in prison, according to the family’s Web site.

Last month, Siamak Namazi, a Dubai-based businessman, was arrested while visiting relatives in Iran, his family said. Any charges against him are unknown.

A former FBI agent and CIA contractor, Robert Levinson, was last seen publicly in March 2007 on the Iranian resort island of Kish, where he was investigating cigarette smuggling on behalf of a client. Iran denies knowledge of Levinson’s whereabouts or any involvement in his disappearance.

A video circulated in December 2011 purported to show Levinson but offered no clear indication of his location. Iran denies that it is holding him.

Read more:

Timeline: Key events in Rezaian’s case

Obama presses Iran to free detained Americans

Full coverage of Jason Rezaian’s imprisonment