Gholian, 28, one of the most prominent women held in Iran and seen as a political prisoner by activists, was first detained in 2018 after reporting on a labour protest in the west of the country.

She was then briefly released on bail but arrested in January 2019 to serve a five-year sentence on national security charges.

A video posted on her Instagram and Twitter accounts showed Gholian, in traditional dress and clutching a bouquet of flowers, triumphantly walking outside the walls of Evin prison in Tehran after her release.

In a sign of defiance, she shouted twice over: "Khamenei the tyrant, we'll drag you into the ground!"

She was also not wearing a headscarf, in defiance of the Islamic republic's strict dress code for women.

"Now I am free, hoping for the freedom of Iran!" Gholian wrote on her Twitter and Instagram accounts.

She expressed hope for the release of other women seen as political prisoners by activists, including the environmental campaigner Niloufar Bayani, the women's rights campaigner Bahareh Hedayat and German-Iranian dual national Nahid Taghavi.

The New York-based Center for Human Rights in Iran (CHRI) hailed Gholian as "a courageous women's and human rights activist" and described Evin as "notorious for holding peaceful prisoners of conscience".

In prison she has, through letters and messages to supporters, become a strong voice against the abuses that she says women are subjected to in Iranian jails

In a lacerating letter published by BBC Persian in January, Gholian described the methods used by interrogators to force confessions and the screams heard within the prison.

"Today the sounds we hear... across Iran are louder than the sounds in interrogation rooms; this is the sound of a revolution, the true sound of 'Woman, life, freedom'," she said, using the main slogan in women-led protests that broke out in Iran six months ago.

Many of the women held in Iran were arrested well before the protests sparked by the September 16 death in custody of Mahsa Amini, a young Iranian Kurd who had been detained for allegedly violating the dress code for women.

But their numbers swelled in the ensuing crackdown.

Several women have been released in recent weeks, including French-Iranian academic Fariba Adelkhah, but campaigners have rejected an amnesty as a PR stunt and key figures remain detained.