Washington Post's Jason Rezaian
Jason Rezaian's trial in Iran was conducted in secrecy with his kin not allowed in the courtroomReuters

Jason Rezaian, who has been convicted in Iran on charges of espionage, is said to be in "immediate danger." The Washington Post correspondent's health is failing following "mistreatment" in Iran, the publication said.

Rezaian, who has been held in Iran's Evin prison since 2014, completes 500 days in prison on 3 December. The Washington Post's executive editor Martin Baron termed it "the grimmest" of milestones. "Five-hundred days robbed of his life, 500 days deprived of his family, 500 days denied any semblance of justice," Baron said.

The 39-year-old journalist was convicted in October on spying charges but there has been no clarification from Iran on how the judgement came to be. Rezaian's trial was conducted in secrecy. His family members were not allowed to attend the hearing by Tehran's Revolutionary Court, which takes up cases that it believes are of importance to the country's national security. The reporter's wife was also detained but later released with two photojournalists who had been arrested along with the couple on 22 July 2014.

According to the Washington Post, Rezaian's brother Ali will submit to Iran's mission to the United Nations a petition with more than 500,000 signatures demanding his "immediate and unconditional release." The publication has also submitted new information about Rezaian with the United Nations Working Group on Arbitrary Detention (UNWGAD) in order to put pressure on Iran.

"Rezaian continues to lose weight; he suffers from blood pressure complications and other physical and mental medical conditions that remain untreated or poorly treated. He has been subjected to further interrogations, psychological abuse, and physical mistreatment," according to the newspaper's latest report on Rezaian. "He is deprived of normal human interactions, forced to wear a hood when he is escorted around the prison by guards or interrogators, and is closely monitored at all times."

The Committee to Protect Journalists (CPJ), which is demanding Rezaian's release, said 30 journalists were jailed in Iran in 2014. Only China jailed more journalists in that year.