US-Iranian journalist Roxana Saberi, who has been detained in Iran since January, has been put on trial for spying for the United States, a spokesman for the judiciary 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," Ali Reza Jamshidi told reporters.

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

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 the charges against Saberi were "baseless."

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

Saberi, 31, was reportedly initially detained for buying alcohol which is prohibited in the Islamic republic.