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.

Jason Rezaian, a dual US-Iranian citizen, has been accused of passing information to "hostile governments".

The Washington Post's editor described the trial as "shameful" and criticised the decision to hold it in private.

Mr Rezaian could face up to 20 years in prison if convicted.

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 says.

"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 imprisoned in Iran's notorious Evin prison - placed in isolation for many months and denied medical care he needed.

It says that he was given only an hour-and-a-half to meet a lawyer approved by the court and "no evidence has ever been produced by prosecutors or the court to support these absurd charges".

The BBC's 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 nuclear negotiations between Iran and the West.

Some analysts have suggested the arrest was related to internal power struggles in Iran over the outcome of the nuclear 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, who was arrested alongside him in July but later bailed, and a third person have also been summoned to appear in court.

By BBC