Iran has charged three US citizens, detained in July, with espionage.
Tehran general prosecutor Abbas Jafari Dolatabadi said: 'The three are charged with espionage. Investigations continue into the three detained Americans in Iran.'
Shane Bauer, 27, Sarah Shourd, 31, and Josh Fattal, 27, were held after they crossed into Iran from northern Iraq at the end of July.
However, their families say they strayed across the border accidentally.
Iranian President Mahmoud Ahmadinejad suggested in an interview with the American television network NBC in September that the Americans' release might be linked to the release of Iranian diplomats he said were being held by US troops in Iraq.
Under Iran's Islamic sharia law, espionage is punishable by death.
US Secretary of State Hillary Clinton said the US believed Iran has no reason to detain the three hikers and that they should be released.
'We believe strongly that there is no evidence to support any charge whatsoever,' Mrs Clinton said on a visit to Berlin.
'And we would renew our request on behalf of these three young people and their families that the Iranian government exercise compassion and release them so they can return home, and we will continue to make that case,' she added.
