An Iranian-American man imprisoned in Iran, Baquer Namazi, has been returned to prison after a brief release due to health concerns.
Lawyer Jared Genser said in a statement that the decision to return his 81-year-old client to Tehran's Evin prison despite the advice of the Iranian government's own medical examiner is "tantamount to a death sentence."
Namazi had undergone surgery while imprisoned to have a pacemaker installed and Genser had wanted his client's leave to be made permanent given his poor health.
The U.S. State Department said it was "incredibly disappointed" with Namazi's return to prison after a four-day leave.
"We have been alarmed for some time at his declining health. We know he's in urgent need for sustained medical care. We're deeply disappointed in the fact he has been returned to prison. We're concerned about his health," spokeswoman Heather Nauert said.
"We call for his unconditional release from his unjust detention in Iran, and that renews our calling for all Americans who are being held in Iran and being held unjustly to be returned to the United States," she added.
Namazi, who is among several dual nationals held by Iran, is serving a 10-year prison sentence after being found guilty in a closed-door trial for spying and cooperating with the U.S. government. He has denied the charges.
Analysts believe Iran is holding Namazi and others as bargaining chips for future negotiations with the West.