An Iranian-American journalist who once worked for a U.S. government-funded broadcaster is believed to have been detained by Iran for months now, authorities said Sunday, further raising the stakes as Tehran threatens to retaliate over an Israeli attack on the country.

Rights groups say journalist Reza Valizadeh has been detained, amid heightened tensions between the United States and Iran.

Rights groups said that Reza Valizadeh, an Iranian-American journalist, was recently arrested in Iran, although the State Department did not confirm that he was the person detained.