U.S. President George W. Bush on Friday urged Iran to release four Iranian Americans detained in the Islamic republic.

"I strongly condemn their detention at the hands of Iranian authorities. They should be freed immediately and unconditionally, " Bush said in a statement.

Journalist Parnaz Azima and academics Haleh Esfandiari, Kian Tajbakhsh, and Ali Shakeri were "being held against their will by the Iranian regime," Bush said.

"Their presence in Iran -- to visit their parents or to conduct humanitarian work -- poses no threat," he said.

It was reported that the three academics are being held in Iran on spying charges, and that the journalist faced similar allegations but had not been arrested.

Bush also demanded Iran provide information on a former FBI agent, Robert Levinson, who reportedly went missing during a private visit to Iran in March.

Washington severed diplomatic relations with Tehran shortly after Iran broke out the Islamic revolution in 1979.

Source: Xinhua