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.

The imprisonment of Reza Valizadeh, acknowledged to The Associated Press by the U.S. State Department, came as Iran marked the 45th anniversary of the American Embassy takeover and hostage crisis on Sunday. It also followed Iran’s Supreme Leader Ayatollah Ali Khamenei threatening both Israel and the U.S. the day before with “a crushing response” as long-range B-52 bombers reached the Middle East in an attempt to deter Tehran.