The Soros Foundation has expressed concern for the safety of a US-Iranian scholar whom it says was detained in Iran earlier this month.
The foundation called for the immediate release of Kian Tajbakhsh.
It said he had been working as its consultant to facilitate public health and humanitarian assistance with the knowledge of the Iranian government.
There has been no confirmation of Mr Tajbakhsh's detention from the authorities in Tehran.
The Iranian intelligence ministry has accused the Soros Foundation - a private organisation that promotes democratic governance and human rights - of issuing propaganda against Iran.
Mr Tajbakhsh is the second Iranian-American national reported to be detained by Iran.
Haleh Esfandiari, the head of the Middle East section of a Washington research institute was also detained this month.
Iran says the institute receives funding from the Soros Foundation.