WASHINGTON (AP) -- The Senate on Monday unanimously passed a resolution calling on Iranian officials to immediately release three Americans held in Iran and help locate a fourth.

The measure, which passed 90-0, calls for Iran to free Saeed Abedini, Amir Hekmati and Jason Rezaian and cooperate with the U.S. government to locate and return former FBI agent Robert Levinson, who is believed to be missing in Iran.

Abedini, a Christian pastor from Idaho, has been in Iranian custody since September 2012 and is serving an eight-year sentence for undermining state security. During a trial in January, he was convicted of trying to establish a network of Christian churches in private homes.

Sen. James Risch, R-Idaho, who introduced the measure, argued that the four should have been released before the U.S. started negotiating a nuclear agreement with Iran.

"Iran thinks it elevates its position in the world because it does these kind of things. It does not," Risch said. "Certainly it shows toughness, but a barbarian type of toughness that the world is not impressed with at all."

Hekmati, a dual U.S.-Iranian citizen born in Arizona, was arrested on spying charges in August 2011. Hekmati, who has family in Michigan, was convicted of spying for the CIA and sentenced to death, but Iranian officials later reduced the sentence to 10 years in prison.

"He is the person that has been waiting longest to come home. He has been tortured and is a locked inside a prison notorious for its deplorable conditions," said Democratic Sen. Debbie Stabenow of Michigan. "This resolution is a clear message to the Iranian government: If you want a seat at the table with the rest of the international community, free Amir Hekmati now as well as all of the other U.S. citizens who are being held as hostages."

Rezaian, The Washington Post's bureau chief in Tehran, has been held since July 2014. Iranian authorities have not provided specific details about why he is being held.

By The Associated Press