A leading Iranian peace activist and American citizen has been freed from prison in Tehran on the eve of president Ahmadinejad's key address to the UN.

President Mahmoud Ahmadinejad said today that it was "too late" to stop Iran's nuclear programme and warned the US and its allies not to push for new UN sanctions.

US academic Haleh Esfandiari and two other Iranian-Americans have been “formally charged” with endangering national security and espionage, Iran’s judiciary spokesman said today.

Iran says it has uncovered spy rings organised by the United States and its Western allies, claiming on state-run television that the espionage networks were made up of “infiltrating elements from the Iraqi occupiers”.

As Iran’s judiciary acknowledged that the country’s intelligence is investigating an American-Iranian academic for security crimes, US Secretary of State blasted the detention and called on Tehran today to immediately release Haleh Esfandiari.