Iranian authorities released a young French academic who was accused of spying on bail yesterday, the French presidency announced, after she spent six weeks in Tehran's notorious Evin jail.

University teaching assistant Clotilde Reiss, 24, was arrested in Tehran on July 1 after being accused of taking part in post-election street protests and was one of more than 100 defendants at a televised mass trial earlier this month.

She will now have to stay at the French embassy in Tehran while she awaits the verdict in her trial, which was heard on August 8. France has demanded that her case, and that against a Franco-Iranian embassy worker, be thrown out.

"The French authorities now demand that the judicial procedures levelled against Clotilde Reiss and Mrs Nazak Afshar - which nothing can justify - be ended as soon as possible," the French presidency said.

According to the statement, France's President Nicolas Sarkozy had spoken to Ms Reiss by telephone and found her "in good health and good spirits".

"He told her of his joy and of the full support she enjoys from him and all French people, who have followed her arrest and the trial to which she was submitted with concern," the statement said.

"He remarked on the dignity and the courage with which Clotilde Reiss has faced up to this test," the statement said.

"She turned 24 on July 30 in Evin prison, which is not an easy prison, which is an unbearable prison, to state things as they are," French Foreign Minister Bernard Kouchner had earlier told French state TV.

Ms Reiss was seized by Iranian authorities at Tehran airport as she tried to fly home after completing a six-month teaching and research assignment in the central city Esfahan.

In the closing weeks of her stay she witnessed some of the street protests that erupted after President Mahmoud Ahmadinejad's disputed re-election.

According to Mr Kouchner, Iranian authorities accused her of spying after she took souvenir photographs of the marches and sent them to friends. State media in Iran have said she has also admitted sending a report to the French embassy.

France has firmly insisted that Ms Reiss is innocent of any espionnage and has demanded her unconditional release, but Iranian prosecutors have said that she must remain in Iran pending the verdict in her case.