Imprisoned Nobel Peace Prize laureate Narges Mohammadi recently underwent complex surgery in Iran, during which part of a bone in her right leg was removed due to cancer concerns.
However, she was swiftly returned to prison, heightening risks to her health, human rights organizations have warned.
In a letter to the United Nations Human Rights Council, signed by more than 40 activist groups, they called for her immediate release on medical furlough, citing her unjust imprisonment on charges that have drawn widespread international condemnation.
This move is part of a broader campaign pressuring Iran to address Mohammadi's detention since her Nobel recognition last year.
In a separate development, reports emerged of another activist setting himself on fire in prison this past weekend to protest his incarceration as Iran continues to grapple with growing internal unrest following years of protests against its theocratic regime.
"We urge that Iranian authorities stop the criminalization of human rights, and refrain from summoning human rights defenders, journalists, and writers to serve their prison sentences while their health situation is precarious," the letter said, dated Monday.
Iran's mission to the United Nations did not immediately respond to a request for comment Tuesday.
Iranian state media, which largely ignored previous campaigns seeking to free Mohammadi, did not immediately report on the letter.
Mohammadi, 52, is serving sentences totaling 13 years and nine months in prison on charges of collusion against state security and propaganda against Iran's government.
She has continued her activism despite numerous arrests by Iranian authorities and spending years behind bars, including supporting the nationwide, women-led protests sparked by the 2022 death of Mahsa Amini.
She suffered multiple heart attacks while imprisoned before undergoing emergency surgery in 2022, the letter says.
In November of this year, her lawyer announced that doctors had found a bone lesion they feared could be cancerous, prompting the surgery she underwent Thursday.
"She was transferred back to prison after only two days, against her doctor's advice and another request from her legal team that she be granted a medical furlough and sentence suspension," the letter said.
"Years of imprisonment and months of solitary confinement have severely compromised Mohammadi's health, leaving her with multiple serious conditions that cannot be addressed through a short, incomplete hospital visit."
Iran's economy has been in tatters for years due to sanctions imposed by the West. Its people are angry over the devaluation of their currency and government corruption, fueling protests and a government crackdown on dissent.
The return of President-elect Donald Trump to the White House this January has raised concerns among some that he may resume his "maximum pressure" campaign on the Islamic Republic.
Concerns are also rising for other imprisoned activists in Iran.
On Saturday, Saeid Gharibi set himself on fire to protest his 15-year sentence and conditions at Shiraz's Adelabad Prison, the New York-based Center for Human Rights in Iran said.
The center quoted his lawyer as saying Gharibi suffered severe burns to his back and hands and has been denied medical care.
Iran has not acknowledged the incident.
Last week, a former journalist with the Voice of America's Farsi service jumped to his death from a building in Tehran to protest the country's supreme leader and the ongoing crackdown on dissent.
