Reuters – Washington Post reporter Jason Rezaian went on trial on espionage charges behind closed doors in Iran on Tuesday, the semi-official Tasnim news agency reported.

The Post's Tehran bureau chief, an Iranian-American, was detained in his home in July and taken to Tehran's Evin prison.

The Iranian authorities have not elaborated on the charges and pressed on with the case in the face of calls for his release from U.S. President Barack Obama, family members and rights groups.

"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," lawyer Leila Ahsan told Tasnim.

His wife and other family members have been barred from attending the Revolutionary Court session, his brother Ali told Reuters Television on Monday.

"I think the only reason you could possibly imagine that the trial would be closed would be to prevent people from seeing the lack of evidence," Rezaian said.

"It's unlike the Iranian court system, Iranian government, to keep things private when they can go out and use propaganda up against people."

Ali Rezaian said the family had hoped that Rezaian's wife, journalist Yeganeh Salehi, and his mother would be allowed to attend the trial. He said his brother had lost 40 pounds in prison.

Rezaian, who is from Marin County, California, was arrested at his home in Tehran alongside his wife and two Iranian-U.S. friends who have not been named.

Salehi was freed on bail while the couple were released. The three have not been publicly charged.

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.

Tehran and six major world powers, including the United States, are trying to meet a June 30 deadline for a final nuclear deal to end a decade-old standoff with the West.

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.

The New York-based Committee to Protect Journalists has called on Iranian authorities to ensure a “fair and transparent trial” for Rezaian.