Washington Post's Jason Rezaian
The Washington Post's reporter Jason Rezaian faces trial in a closed court in IranReuters

The trial of a Washington Post reporter accused of being a spy has begun behind closed doors in Iran.

American-Iranian journalist Jason Rezaian was to appear before a Revolutionary Court in Tehran, facing charges of espionage, propaganda against the Islamic republic and collaborating with hostile governments.

Rezaian, 39, was serving as the Post's Tehran bureau chief when he was arrested, along with his journalist wife, Yeganeh Salehi, and two other colleagues at the end of July 2014.

All were later released except for the 39-year-old, who has since been detained in Iran's infamous Evin prison.

Washington Post executive editor Martin Baron said Rezaian was denied medical care and proper access to a lawyer, describing the trial as "shameful".

"No evidence has ever been produced by prosecutors or the court to support these absurd charges. The trial date was only disclosed to Jason's lawyer last week. And now, unsurprisingly but unforgivably, it turns out the trial will be closed," Baron wrote in a statement.

"There is no justice in this system, not an ounce of it, and yet the fate of a good, innocent man hangs in the balance. Iran is making a statement about its values in its disgraceful treatment of our colleague, and it can only horrify the world community."

The US government has been so far unsuccessfully pressing for his release, with White House press secretary Josh Earnest also describing charges against the reporter as "absurd".

If convicted, Rezaian could face up to 20 years in jail. His wife is facing related charges in a separate trial.

The trial comes weeks before the deadline for a conclusive deal on Iran's nuclear programme, following the landmark preliminary agreement reached between Tehran and the P5+1 powers – the United States, Britain, France, China, Russia and Germany.

The deal, part of reformist President Hassan Rouhani's less confrontational policy towards the West, has caused some rifts within the theocratic regime, with some analysts suggesting Rezaian might have become a pawn in a power struggle between moderate and hard-line conservative forces.