By Roger Hardy
BBC Middle East analyst
A prominent US think-tank has said that one of its researchers has been detained in the Iranian capital Tehran.
Haleh Esfandiari is one of the leading US authorities on Iran
The Woodrow Wilson Centre has said that Iranian-American academic Haleh Esfandiari had been repeatedly questioned by intelligence officials.
Ms Esfandiari, one of Washington's best known experts on Iran, was visiting Tehran to see her 93-year-old mother.
The incident comes at a time of continuing tension between the United States and Iran.
In December, as she was on her way to the airport to return to the United States, her taxi was stopped by three men who stole her belongings, including her Iranian and US passports.
When she went to replace her passport, she was sent to the intelligence ministry where she was repeatedly questioned about her work at the Woodrow Wilson Centre in Washington.
On Tuesday - after effectively being prevented from leaving the country for more than four months - she was taken to the notorious Evin Prison in Tehran.
The Iranian authorities appear to be particularly suspicious currently of attempts by the Bush administration to promote democratic change in Iran.
In making public the plight of Ms Esfandiari, the director of the Wilson Centre, veteran Democrat politician Lee Hamilton, has emphasised that the centre promotes debate about Iran - reflecting a wide range of views - and receives no government money to influence Iranian policies.