Iran has officially confirmed it has detained an Iranian American in Tehran a week after the United States demanded his release and the release of three other Iranian-Americans.

A foreign ministry spokesman confirmed the detainment of Ali Shakeri, a peace activist from California Sunday.

Iranian officials previously accused three of the dual nationals of endangering national security, but no information has been given about Shakeri.

President Bush has called for the detainees to be freed "immediately and unconditionally."

He said the four pose no threat to Iran. He noted they were in Iran either to visit family or conduct humanitarian work.

Some information for this report was provided by AP and Reuters.