Arash and Kamyar Alaei were respected for their HIV work
Two prominent Iranian Aids doctors have been jailed for a total of nine years for their part in an alleged coup plot.
Brothers Arash Alaei and Kamyar Alaei were accused of being "key elements" in a plan Iran said was backed by the CIA.
The prison sentences were imposed after a secret trial and have provoked strong protests from human rights groups.
Lawyers for the men, known for their pioneering research into HIV and Aids treatment and prevention, said they had strenuously denied all the charges.
They said Arash Alaei was sentenced to six years in prison and Kamyar Alaei to three years.
The men were arrested in June but the reason for their detention was not immediately made clear.
The coup allegations only surfaced in recent weeks.
Iran's state media quoted the Intelligence Ministry as saying the men were among four people engaged in "creating social crisis, street demonstrations and ethnic disputes".
The two other defendants have not been named.
Lawyer Massoud Shafiie said he would appeal against the charges and ask for the brothers' release, "as there is no evidence proving their accusations".
"Their foreign cooperation and relations were only scientific and cultural and not against the country," he said.
The two doctors had travelled widely outside Iran, including to the US, to take part in conferences on HIV/Aids.
The BBC's Jon Leyne in Tehran says this may have meant they fell foul of a law banning Iranians from having relations with so-called "hostile states".
"We don't know why they were targeted," said Sarah Kolloch of US-based Physicians for Human Rights (PHR).
"Most of their presentations were about innovative work in Iran on HIV prevention. If anything, Iran should have been excited that something positive like this was coming from Iran."
The Iranian government has repeatedly warned of attempts to stir up a "velvet revolution" by creating social unrest in the country to destabilise the government.
But no evidence has been produced to show that Arash and Kamyar Alaei were engaged in anything other than international collaboration to fight the spread of HIV and Aids, says our correspondent.