The jailed Iranian Nobel peace prize winner Narges Mohammadi is fighting for her life after being hospitalised under guard for the last five days with a heart condition, her supporters have said.

“We are not just fighting for the freedom of Narges, we are fighting so that her heart continues to beat,” said her Paris-based lawyer Chirinne Ardakani at a news conference of her supporters, adding that the 2023 laureate was now “between life and death”.

Jonathan Dagher of the Paris-based press freedom group Reporters Without Borders (RSF), which is also part of her support committee, said: “This is the first time we are saying that she is between life and death, that there is a risk of death.”

“We must act before it is too late,” he added.

Mohammadi, 54, who has spent much of the past two decades in and out of prison for her activism, was arrested most recently in December after denouncing the Islamic republic at a funeral for a lawyer.

Already suffering from a heart condition, she had two suspected heart attacks on 24 March and 1 May in prison in Zanjan in northern Iran, according to her supporters.

After the most recent incident, she was rushed to hospital for treatment but remains under constant guard, Ardakani said, adding that Mohammadi was experiencing an “unprecedented degradation” of her health. “We have never been so afraid for Narges’s life; she could leave us at any moment.”

Mohammadi has lost 20kg (44lbs) in prison, has difficulty speaking and was “unrecognisable” from before her latest arrest.

Her supporters want Mohammadi to be transferred to Tehran for treatment by her personal medical team but there has been no sign of her being moved from Zanjan.

Mohammadi’s twin teenage children and husband live in Paris and Ardakani urged the French foreign ministry and president, Emmanuel Macron, to take a tougher line on her case. “We are expecting [Macron] to take a strong position. I don’t think this is something excessive,” she said.