US-Iranian journalist Roxana Saberi, who has been detained in a Tehran jail since January, has been put on trial on charges of spying for Iran''s arch-foe the United States, an official said on Tuesday.

"Yesterday, the first session of the trial was held and she was given an opportunity to speak in the court to present her defence," judiciary spokesman Ali Reza Jamshidi told reporters.

He said Saberi, who has been held in the notorious Evin prison in Tehran, is accused of "spying for foreigners... for America."

Saberi, a 31-year-old with dual Iranian-US nationality, risks the death penalty if convicted.

Iran''s decision to put Saberi on trial comes despite calls by US Secretary of State Hillary Clinton for her release and US President Barack Obama''s diplomatic overtures to Iran.

Jamshidi said the verdict was expected in one or two weeks.

He also dismissed remarks by US State Department spokesman Robert Wood who said last week that the charges against Saberi were "baseless."

"It is really funny that someone comments on a case without even seeing it," Jamshidi said.