Saberi, who has US and Iranian nationality and has lived in Iran for six years, has been detained in the Evin prison in Tehran, the capital, since she was arrested in January.

'Apply justice'

Mahmoud Ahmadinejad, the Iranian president, sent a letter to Tehran's chief prosecutor on Sunday instructing him to personally ensure that "suspects be given all their rights to defend themselves".

"Prepare for the court proceedings ... to observe and apply justice precisely,'' the state news agency Irna quoted him as saying.

"Leaders of wisdom must not allow this young woman to be a pawn in a bigger debate and lose focus on so many possibilities"

Rev. Jesse Jackson,
civil rights activist

Saberi has reported for the US-based National Public Radio, the BBC and Fox News.

Her press credentials were revoked in 2006 and she was initially accused of working "illegally", but last week the charge was changed to that of spying for foreigners.

Barack Obama, the US president, said that he was "gravely concerned" about the jailed journalist's safety and was confident that she was not a spy.

"We are working to make sure that she is properly treated and to get more information about the disposition of her case, he said.

Saberi's case has been an obstacle in US-Iran relations at a time when Obama is offering to start a dialogue between the countries.

Hassan Ghashghavi, Iran's foreign ministry spokesman, has denied that Saberi was being used as a bargaining chip in any talks with Washington or to secure the release of Iranian diplomats held by US forces in Iraq.

"The issue of our diplomats is a whole different matter from the trial of an Iranian national such as Miss Saberi," he said.

Appealing to Iran

Meanwhile, Jesse Jackson, a prominent civil rights activist, said he wanted to travel to Iran with a delegation to personally appeal for Saberi's release.

"We need all those that have a voice to help us appeal to Iran to please let her go," he said during a visit to Malaysia.

"Leaders of wisdom must not allow this young woman to be a pawn in a bigger debate and lose focus on so many possibilities."

Human rights groups have repeatedly criticised Iran for arresting journalists and suppressing freedom of speech.

Tehran has arrested several Iranian-Americans in the past few years, accusing them of trying to overthrow the government through what it calls a "soft revolution".

Except for Saberi, they were never put on trial and were eventually released.