Mohammadi has spent much of the past decade in an out of jail and is currently serving a 10-year sentence. She was awarded the Nobel Peace Prize last month.

Mohammadi is suffering from heart- and lung-related ailments, but the prison authorities are not moving her to a hospital for her refusal to wear a hijab, the Islamic head-covering for women, according to reports.?

In Iran, women are required to wear hijab in public. The law was imposed on women after the Islamic Revolution of 1979 overthrew the pro-West liberal monarchy in the country and established a theocratic Islamic regime under the Supreme Leader of Iran.?

Another activist, lawyer Nasrin Sotoudeh, who was arrested for attending the funeral of a teenage girl who died in mysterious circumstances from injuries sustained while not wearing hijab, is also in need of medical care but is being denied it, according to Associated Press (AP).

Both Mahammadi and Sotoudeh are lodged at the notorious Evin Prison in Iran.?

Mohammadi's family described her as suffering from blockages in three veins and lung pressure, reported AP. The Free Narges Mohammadi campaign, citing a statement from her family abroad, said she sent a message on Monday and "informed her family that she started a hunger strike several hours ago".

"Narges went on a hunger strike today ... protesting two things: The Islamic Republic's policy of delaying and neglecting medical care for sick inmates, resulting in the loss of the health and lives of individuals. The policy of death' or mandatory hijab' for Iranian women," the statement read, as per AP. It further said the Islamic Republic "is responsible for anything that happens to our beloved Narges". It later described Mohammadi as "only consuming water, sugar and salt" while refusing to take medicine.

The Norwegian Nobel Committee said it was "deeply concerned" about Mohammadi's health.

"The requirement that female inmates must wear a hijab in order to be hospitalized, is inhumane and morally unacceptable. Narges Mohammadi's initiation of a hunger strike demonstrates the seriousness of the situation. The Norwegian Nobel Committee urges the Iranian authorities to provide Narges Mohammadi, and other female inmates, with whatever medical assistance they may need," said Berit Reiss-Andersen, the chair of the committee, as per AP.

Mohammadi serves as the Vice President of the Defenders of Human Rights Center in Iran. BBC News noted that she has so far been arrested 13 times and has been convicted five times and sentenced to a total of 31 years in prison. The report further said that she has also been sentenced to 154 lashes, but if it's not clear if the punishment has been carried out.?

The AP described Mohammadi as a "leading light" for the nationwide women-led protests in Iran following the death of Mahsa Amini, the 22-year-old woman who died from torture in the custody of the country's infamous morality police. She was detained for an alleged violation of the country's hijab rule while she was out with her brother in a car. Mohammadi's fellow prisoner Sotoudeh, 60, is in jail for attending the funeral of a 16-year-old girl, Armita Geravand, who died mysteriously from injuries sustained while she boarded a train without hijab. Activists have said that the girl could have been attacked for not wearing hijab.