President Nicolas Sarkozy is working to secure the release of a French teaching assistant, who is a defendant in a mass trial in Iran, the president's office said.

An Iranian court has charged Clotilde Reiss, 24, along with dozens of other detainees of spying and helping a Western plot to overthrow the government.

"The president of the republic is following Clotilde Reiss's case very carefully," an official in Sarkozy's office said.

"He is increasing his contacts with people who have the influence to bring this affair to a rapid conclusion and secure her release. That is the main priority in this case," he added.

France has denied that Reiss was a spy.