Human rights lawyer Nasrin Sotoudeh, seen by campaign groups as Iran's highest profile political prisoner, was freed on Wednesday, in another sign that hardline policies may be easing under a new president.
Other prisoners linked to the mass protests after the disputed 2009 re-election of President Mahmoud Ahmadinejad were also freed, opposition website Kaleme reported, raising hopes among activists for a possible reconciliation between Iran's conservative religious leadership and its pro-reform critics.
"I am free from prison today and I am glad but I am worried for my friends in prison," Sotoudeh told CNN by telephone from Tehran, adding that she was "free forever", not on temporary release, and planned to resume her legal career.
Arrested in September 2010, Sotoudeh was serving a six-year term for spreading propaganda and conspiring to harm state security.
Sotoudeh, 50, who defended journalists and rights activists including Nobel Peace laureate Shirin Ebadi, went on hunger strike for nearly 50 days last year to force authorities to repeal a travel ban on her young daughter.
With fears that she might die, the United States was among the countries criticizing Iran and demanding Sotoudeh be freed.
The prison releases come less than a week before President Hassan Rohani addresses the UN General Assembly for the first time and is expected to present a less confrontational image than Ahmadinejad, under whose eight years in power Iran came under ever-tougher Western trade sanctions.
Rohani won a surprise victory over hardline rivals in June, pledging to ease some political and social restrictions, and his supporters have called for the release of political prisoners.
Kaleme said one of those released on Wednesday was Mohsen Aminzadeh, a former deputy foreign minister under reformist former President Mohammad Khatami, who supported reformist presidential candidate Mir Hossein Mousavi in 2009.
Feizollah Arabsorkhi, a former deputy minister of commerce under Khatami, was also released, the website said. The total number of prison releases was not immediately clear, but various news reports mentioned seven other women and three men in total.
Sotoudeh's release comes one day after Supreme Leader Ayatollah Ali Khamenei said he supported "flexibility" in Iranian diplomacy, a rare signal that he might endorse a shift in Tehran stance in its problematic relations with the West.
"It's a humanitarian gesture and also it's a smart political move, mainly because of the signal it sends to the U.S. Congress, which still cares about the human rights conditions in Iran," Yasmin Alem, a senior fellow at the Atlantic Council's South Asia Center, said of the prison releases.
"But I wouldn't read too much into at least this initial release of political prisoners."
Authorities, who transferred Sotoudeh from Tehran's Evin jail on Wednesday evening to her home, gave no reason for the release and offered no details on who had ordered it, Sotoudeh's husband Reza Khandan told Reuters.
"They just told her: 'You're free, go'," he said.
When asked if her release signaled a "new day" for Iran, Sotoudeh told CNN: "It is soon to say new day because we have many political prisoners in prison, but I hope this will be a new day."