text: Jason Rezaian, a dual US-Iranian citizen, has been accused of passing information to "hostile governments".
  He defended himself in court, saying he had carried out his activities as a journalist, Iranian media reported.
  Mr Rezaian could face up to 20 years in prison if convicted.
  He is being tried in one of Tehran's revolutionary courts, usually reserved for political cases or those related to national security.
  Mr Rezaian appeared in court alongside his wife, Yeganeh Salehi, and a third detainee, reported to be a female photojournalist.
  The judge, Abolghassem Salavati, outlined the charges against Mr Rezaian as "espionage through collecting classified information and providing it to hostile governments" and "spreading propaganda against the regime", Iran's Mehr news agency reported.
  Mr Rezaian rejected some of the charges, Mehr reported, saying: "I am a journalist and I carried out all my activities legally and as a journalist."
  The presiding judge, Abolghassem Salavati, is known for handing down harsh sentences and is accused by human rights groups of cracking down on journalists and activists.
  He has been dubbed the "judge of death" for imposing several death sentences after the 2009 post-election opposition protests.
  He first came to public attention in 2006 when he sentenced two defendants to death for the murder of Hassan Moghadas, the Revolutionary Court judge who sentenced a prominent journalist - Akbar Ganji - to 15 years in jail.
  Since then, Mr Salavati has presided over or sat in the trials of several prominent political figures, including a daughter of former President Akbar Hashemi Rafsanjani.
  In January 2009, he found four people guilty of conspiring with the US government against Iran in their work on an HIV prevention programme.
  In September 2014, Mr Salavati sentenced Mohsen Amir-Aslani to death for heresy for his interpretation of the Jonah and the Whale story as a symbolic tale.
  Source: BBC Monitoring's Armen Shahbazian
  What are Iran's revolutionary courts?
  The US State Department repeated its call for the "absurd charges" to be dropped.
  Iran has not recently commented on the case, but the Washington Post has spoken out forcefully.
  "The shameful acts of injustice continue without end in the treatment of [Mr] Rezaian," a statement by the newspaper's Executive Editor Martin Baron said on Monday.
  "Now we learn his trial will be closed to the world. And so it will be closed to the scrutiny it fully deserves.
  "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."
  The paper points out that Mr Rezaian was arrested without charge and jailed in Iran's notorious Evin prison - placed in isolation for many months and denied medical care he needed.
  His brother, Ali, meanwhile told the BBC there was no evidence to support the charges: "They've cherry-picked information to come up with whatever they could to charge him with to make it seem like there was a reason that they've held him."
  The BBC's US state department correspondent, Barbara Plett Usher, says US officials have repeatedly raised his case during months of nuclear negotiations with Iran, but have declined to link the two.
  The imprisoned journalist's family have taken heart from recent comments by President Barack Obama, who said that the White House would not rest until Mr Rezaian was brought home safely, our correspondent adds.
  The case is all the more sensitive because it has unfolded during negotiations between Iran and the West over the country's nuclear programme.
  Some analysts have suggested the arrest was related to internal power struggles in Iran over the outcome of the talks.
  Iran and six major world powers, including the US, have set a 30 June deadline for a conclusive nuclear deal to end a 10-year impasse.
  Mr Rezaian had been the Washington Post's Tehran bureau chief since 2012.
  His wife, Yeganeh Salehi, was arrested alongside him in July but later bailed after spending two and a half months in custody.
  It is not clear when the next trial session will be held.
target: The trial of a Washington Post journalist detained in Iran for almost 10 months on charges that include "espionage" has opened in the capital Tehran behind closed doors.