Foreign Minister Manouchehr Mottaki did not say when proceedings would begin or specify the charge other than to say the Americans had "suspicious aims." In November, however, authorities accused the Americans of spying.
There are concerns in the U.S. that Iran could use them as bargaining chips in talks over its nuclear program or in seeking the return of Iranians they say are missing.
Relatives and the U.S government say the three were innocent tourists on a hiking trip in northern Iraq and accidentally crossed into Iran, where they were arrested on July 31.
"They will be tried by Iran's judiciary system and verdicts will be issued," Mottaki said at a news conference, without elaborating in detail. He said the three were still being interrogated.
Even if the Americans are tried, however, there is still a chance they could be released fairly soon.
Iranian-American journalist Roxana Saberi was convicted of espionage and sentenced to eight years in prison, before she was released on an appeal in May. Canadian-Iranian journalist Maziar Bahari of Newsweek was released in October on bail and allowed to leave the country after being swept up in the post-election crackdown on street protests. The Americans — Shane Bauer, 27, Sarah Shourd, 31, and Josh Fattal, 27 — were detained by Iranian authorities after crossing an unmarked border from northern Iraq.