US Secretary of State Hillary Clinton has urged Iran to free three Americans as soon as possible after Tehran announced they would be put on trial.
The BBC reports the group of hikers has been held since July after they crossed the border from Iraq. They have been accused of entering Iran illegally.
Iranian officials have also stated that Shane Bauer, Sarah Shourd and Josh Fattal were spying.
Their families say they were hiking and strayed across the border accidentally.
Iran's foreign minister said the three were still being interrogated.
The decision to try the Americans comes less than a month after Iran released five British sailors whose racing yacht had crossed into Iranian waters.
