By Frances Harrison
BBC News, Tehran
Iran has officially confirmed that it is detaining a fourth Iranian American on suspicion of spying.
Mr Shakeri disappeared when he was due to fly out of Iran
Ali Shakeri, an American Iranian peace activist and academic disappeared while on a visit to Iran last month but officials initially denied his arrest.
These arrests of dual nationals have sent shock waves through the huge Iranian diaspora.
They have also prompted many academics to think twice about attending conferences in Iran.
Iran's Foreign Ministry spokesman Mohammad Ali Hosseini confirmed that the government is holding Ali Shakeri and investigating him for charges of spying.
He is the third American academic of Iranian origin to be jailed in Iran in the last month.
Call for release
Like many of the others he came to see relatives here but when he was due to fly out Mr Shakeri disappeared.
His luggage was later collected from the airline.
For weeks the authorities denied any knowledge of Mr Shakeri's whereabouts but now they have finally confirmed he is in detention.
Iran has also jailed and charged with spying two well-known American Iranian academics - Haleh Esfandiari and Kian Tajbaksh.
And an American Iranian journalist working for Radio Free Europe has been prevented from leaving the country and is to be charged with cooperating with what the authorities call counter-revolutionary radio stations.
But Iran has denied holding another American - a former FBI agent who disappeared after visiting an Iranian duty free island in the Gulf in March.
The US president George Bush has called for the immediate and unconditional release of those being held - denying charges that they were spying for the United States.