Iran's intelligence minister has said there is evidence that three US hikers it is holding had links to intelligence agencies, according to Iran's Press TV.
The families of the hikers, who Iran has held in jail since last July, say they strayed across the border accidentally while hiking in Iraq.
Heydar Moslehi said the evidence would soon be made public, the report said.
Officials have accused Shane Bauer, Josh Fattal and Sarah Shourd, all in their 20s and 30s, of illegal entry.
Iranian officials have also previously alleged that the three were spying.
"It is evident to us that the three Americans were in contact with intelligence services. But it is up to the judiciary to decide how to deal with the case," Mr Moslehi said in an interview with the state-funded television channel.
The channel also reported he had said there was "compelling evidence", but did not provide details.
HIGH PROFILE DETENTIONS
25 November: Five Britons arrested after their racing yacht strays into Iranian waters. Freed a week later.
Jan 09: US-Iranian journalist Roxana Saberi arrested and jailed for spying in April, but released a month later after an appeal.
23 March 07: 15 Royal Navy personnel seized by Iranian warships after searching a cargo boat in the Gulf. Held for nearly two weeks.
In December Iranian Foreign Minister Manouchehr Mottaki said the hikers would stand trial, but he did not specify on which charges.
The families said in a joint statement that Mr Moslehi's allegations were "totally unfounded".
"Allegations that they are spies are ridiculous... Our loved ones' continued detention and the psychological stress they are made to endure are unjustified and we again appeal to Iran to allow them to return home," the statement said.
US Secretary of State Hillary Clinton has called on Tehran to free the hikers, and said that any charges would be unfounded.
The three Americans were seized by Iranian border guards on 31 July near the town of Marivan, and are being held in Tehran's Evin prison.
The three hikers are all friends who attended the prestigious University of California, Berkeley.