Iranian-American Baquer Namazi arrived Wednesday in the United Arab Emirates to receive medical care after being allowed to leave Iran.
U.S. Secretary of State Antony Blinken said in a statement that 85-year-old Namazi "has asked that we convey his deepest thanks to all of those who worked so tirelessly to secure his release."
Iran convicted the former United Nations official of collaborating with a hostile government in 2016 and sentenced him to 10 years in prison before releasing him to house arrest on medical grounds in 2018.
Blinken said Namazi was "wrongfully detained" and that the United States remains committed to freeing "all remaining wrongfully detained U.S. citizens in Iran and around the world."
Namazi's son, Siamak, was also convicted in 2016 on the same charges, which the United States described as baseless for both men.
Another son, Babak Namazi, said in a statement released by the family's lawyer that news of his father's release was bittersweet; his brother and other Americans remain in Iranian detention.
Some information for this report came from The Associated Press, Agence France-Presse and Reuters.