The United States on Wednesday said it was "deeply concerned" that Iran had returned Iranian-American Baquer Namazi to prison after briefly releasing him so he could receive medical treatment.
The White House said it understood that the 81-year-old former U.N. official was returned to Iran's "notorious Evin Prison against the strong advice of his doctors and the Iranian regime's own medical examiner."
Namazi is serving a 10-year sentence based on Tehran's allegations that he spied against Iran and cooperated with the United States. The United States has called those charges "false."
The White House said Namazi has been hospitalized four times in the last year and "continues to suffer from life-threatening heart problems. He remains in urgent need of sustained medical care."
The White House said it "holds Iran fully accountable for his well-being."
The Trump administration called for "the immediate and unconditional release of all unjustly detained and missing U.S. citizens in Iran," including Namazi, his son, Siamak Namazi, Xiyue Wang and Robert Levinson.
Baquer Namazi was detained two years ago, five months after his son was arrested.
Jared Genser, an attorney for the Namazi family, said returning the elder Namazi to prison was "tantamount to a death sentence."
Babak Namazi, another son, told reporters in Washington his father's renewed imprisonment was a "spectacular display of cruelty" by the Iranian government.