She was speaking after Iranian Foreign Minister Manouchehr Mottaki said the three would stand trial, although he did not specify on which charges.

US Secretary of State Hillary Clinton has called on Tehran to free three US citizens who crossed into Iran while hiking in Iraq.

Iranian officials have also previously alleged the trio were spying.

Mrs Clinton said that any charges would be unfounded.

Shane Bauer, Sarah Shourd and Josh Fattal were detained in July and have been accused of illegal entry.

"We consider this a totally unfounded charge. There is no basis for it... They were out hiking and unfortunately, apparently, allegedly walked across an unmarked boundary."

Their families say they strayed across the border accidentally.

Mrs Clinton said: "We appeal to the Iranian leadership to release these three young people and free them as soon as possible.