Iran ? Iran has released an Iranian-American democracy scholar who spent four months in prison – the third time in recent weeks Tehran has set free dual citizens it accuses of trying to stir up a revolution.

Kian Tajbakhsh, an urban planning consultant with the Soros Foundation’s Open Society Institute, was released late Wednesday, Iran’s official news agency, IRNA, reported Thursday.

He was one of four Iranian-Americans charged with endangering national security – an accusation they and their employers denied.

The charges have increased tensions between the United States and Iran, already high over U.S. accusations that Iran is seeking to develop a nuclear weapons and is fueling violence in Iraq. Iran denies both claims.

But in recent weeks, Iran has shown a change of heart toward the case. Last month, Iranian-American academic Haleh Esfandiari was also released from the Evin prison where Tajbakhsh, 45, was held. She has since returned to the United States.

On Tuesday, Iran allowed a third Iranian-American, journalist Parnaz Azima, to leave the country after being trapped since authorities confiscated her passport in January. There has been no word on Ali Shakeri, a fourth Iranian-American detained on the security-related charges.