A US-Iranian academic detained in Iran last week is being investigated for suspected "security" crimes, officials in Tehran have said.
Haleh Esfandiari is one of the leading US experts on Iran
Haleh Esfandiari, 67, was being held in Tehran's Evin prison, Iranian judiciary spokesman Ali Reza Jamshidi said.
Mr Jamshidi said the investigation was still going on, without giving any further details.
The US has condemned the arrest of Ms Esfandiari, who works at the Woodrow Wilson Centre in Washington.
The incident comes at a time of continuing tension between the United States and Iran over Tehran's controversial nuclear programme.
"[Ms Esfandiari] is right now under the authority of the intelligence ministry," Mr Jamshidi told reporters in Tehran.
"Her crime is security issues," the spokesman added.
Ms Esfandiari - one of Washington's best known experts on Iran - was visiting the Iranian capital to see her 93-year-old mother.
She was detained on 8 May, after being prevented from leaving Iran for several months.
In December, as she was on her way to the airport to return to the US, 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.
The Iranian authorities appear to be particularly suspicious currently of attempts by the Bush administration to promote democratic change in Iran, says the BBC's Middle East analyst, Roger Hardy.
In making public the plight of Ms Esfandiari, the director of the Wilson Centre, Lee Hamilton, said last week that the centre promoted debate about Iran - reflecting a wide range of views - and received no government money to influence Iranian policies.