Nobel Peace Prize winner Narges Mohammadi has begun a hunger strike in her Iranian prison in protest at limits on medical care for her and other inmates, as well as the obligation for women to wear the hijab in the Islamic republic, her family said on Monday.

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".

"Narges Mohammadi, today, through a message from Evin Prison, has informed her family that she started a hunger strike several hours ago. We are concerned about Narges Mohammadi's physical condition and health," her family said in a statement.

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.

Prison authorities in response have refused to transfer Mohammadi, who suffers from heart and lung conditions, to a hospital outside Evin for treatment.

The family said in the statement that she was in "urgent" need of medical treatment outside prison.

"Narges went on a hunger strike today in protesting two things: The Islamic Republic's policy of delaying and neglecting medical care for sick inmates... (and) the policy of 'mandatory hijab' for Iranian women," the statement said.

"The Islamic republic is responsible for anything that happens to our beloved Narges," it said. "It's been a week now that they are refusing to give her the medical aid she needs."

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.