Image caption Sarah Shourd was released from Iran after months of pressure by the US

US woman Sarah Shourd, who was released by Iran after being detained with two fellow US hikers in 2009, has said she will not return there to stand trial.

Ms Shourd was to stand trial next week for espionage alongside her friends, who are still being held in Iran.

She told the BBC she suffered from post-traumatic stress disorder and returning would be "too traumatic".

She and the other hikers have said they unknowingly crossed into the country while hiking in July 2009.

Ms Shourd was released on bail in September 2010 and returned to the US. Her fiance Shane Bauer and their friend Josh Fattal remain in prison in Tehran.

Mr Bauer and Mr Fattal pleaded not guilty at the first session of their trial in February 2011, with the second session scheduled for 11 May. Ms Shourd pleaded not guilty in absentia.

Prosecutors said they had evidence the three were connected to US intelligence agencies.

"The moment I relive the most is having to leave Shane and Josh over seven months ago," Ms Shourd said.

"Seeing their faces and the hope they had at that point - that they would soon be released - is the most painful thing for me, up until this day," she added.

'Too traumatic'

Ms Shourd said she was diagnosed with post-traumatic stress disorder by clinical forensic psychologist Barry Rosenfeld and that a five-page psychological evaluation had been sent to the Iranian Revolutionary Court.

The Iranian court had not responded to her refusal to return for the trial, she said.

"There's a part of me that would like to go and stand by Shane and Josh and defend our innocence together," she said.

"But I'm afraid that after what I've been through, going back would be too traumatic for me."

Ms Shourd, who was released after months of pressure by the US, has said the trio were hiking in Iraqi Kurdistan and did not intentionally stray over the border with Iran, where they were arrested by soldiers.

They had visited the tourist village of Ahmed Awa, she said, and hiked along a trail local residents had recommended.