Washington Post Reporter Jason Rezaian Goes On Trial Behind Closed Doors In Tehran

* Session adjourned after over two hours - IRNA

* Wife and a photojournalist on trial alongside Rezaian

* Lawyer says Rezaian charged with espionage

* U.S. says closed trial a concern, calls for release (Adds State Department comment)

DUBAI, May 26 (Reuters) - Washington Post reporter Jason Rezaian went on trial on espionage charges behind closed doors in Tehran on Tuesday, 10 months after he was arrested at his home and imprisoned, Iran's semi-official Tasnim news agency reported.

His wife, Yeganeh Salehi, and a woman described as a photojournalist also went on trial, the official IRNA news agency said. Both women were detained with him in July but later released.

The three, all American-Iranian, were in court for around two hours before the session was adjourned, IRNA added.

Iranian authorities have not released details of any charges and pressed on with the case despite calls from U.S. President Barack Obama, family members and rights groups for Rezaian's release and more information on the charges.

The case has put pressure on U.S.-Iranian relations, while Tehran, Washington and five other world powers have been trying to hammer out a deal to end a decade-old standoff over Iran's nuclear program.

The closed trial "adds to our concerns and fits, unfortunately, into a pattern of a complete lack of transparency and lack of due process that we've seen" since Rezaian's detention, State Department Jeff Rathke told reporters at a daily briefing in Washington.

The United States again called for dismissal of the "absurd" espionage charges against Rezaian, Rathke said.

Rezaian's lawyer Leila Ahsan told Tasnim that "he has been charged with espionage for collecting confidential information ... and handing it to hostile governments, writing a letter to Obama and acting against national security."

Rezaian's brother Ali, in an interview with MSNBC, said the family learned the court adjourned but little else.

"We know that he was planning to go in and put on a strong defense, let everybody know that he's not guilty, that he's innocent of all these charges," he told the U.S. television network, speaking from the Washington-based National Press Club, which along with other journalism groups is supporting Rezaian and is backing a petition demanding his release.

Ali earlier told Reuters Television that his brother, the Post's Tehran bureau chief, had lost 40 pounds (18 kg) in prison.

Rezaian was arrested with his wife and two other Iranian-American friends, the female journalist and a man. Salehi was freed on bail while the couple were released and none of them have been publicly charged. There was no information on the man in Tuesday's reports.

Douglas Jehl, the Post's foreign editor, called the charges baseless. "What Jason did was act as a journalist, which involves gathering information, verifying information, and ultimately publishing it," he told Reuters Television.

Obama has called the charges against Rezaian "vague" and pressed Iran to release all American detainees.

Iranian Foreign Minister Mohammad Javad Zarif said in April that an intelligence operative, possibly linked to the U.S. government, may have "taken advantage" of Rezaian. (Additional reporting by Susan Heavey, Bill Trott and Nadine Alfa in Washington; Editing by Andrew Heavens and Jonathan Oatis)