The family of imprisoned Iranian Nobel Peace Prize winner Narges Mohammadi says she has ended a hunger strike after she received medical treatment without wearing the obligatory head covering.

In a message posted on her Instagram account Thursday, the activist's family said she was transferred to a hospital for exams on Wednesday. She suffers from heart and lung conditions.

"After being transferred to the hospital without wearing the compulsory hijab and returning to the women's ward, I ended my hunger strike," she was quoted as saying in the statement.

Veteran rights activist Mohammadi, 51, currently held in Tehran's Evin prison, was awarded the Nobel prize in October "for her fight against the oppression of women in Iran".

Her family said on Monday that Mohammadi had begun a hunger strike in protest at limits on medical care for her and other inmates, as well as the requirement for women in the Islamic republic to cover their hair in public.

Friends and allies, who had gathered to visit Mohammadi at the hospital, were "threatened and harassed by Islamic Republic Security forces," her supporters also said Thursday.

Mohammadi is refusing under any circumstances to wear a hijab, the head covering which has been obligatory for women in public spaces since shortly after Iran's 1979 Islamic revolution.

She vowed to continue to refuse to wear a headscarf.

"Until the abolition of the 'forced hijab,' I will continue to walk like this on the streets, and you will tremble at the sight of us women without the 'forced hijab,'" she was quoted as saying.

First arrested 22 years ago, Mohammadi has spent much of the past two decades in and out of jail over her campaigning for human rights in Iran.

She has most recently been incarcerated since November 2021 and has not seen her children, now based in France, for eight years.

Mohammadi's Nobel came in the wake of months-long protests across Iran triggered by the September 2022 death in custody of Mahsa Amini, 22, who had been arrested for allegedly flouting the Islamic republic's strict dress rules for women.