Mohammadi, who has spent much of the past decade behind bars, was released from Tehran's Evin prison in December for a limited period on medical leave, with her legal team repeatedly warning that she could be re-arrested at any time.

Norwegian Nobel Committee chair Jorgen Watne Frydnes said in a statement he had received an "urgent phone call" from Mohammadi, 53, who said her life was now in danger.

"The clear message, in her own words, is that 'I have been directly and indirectly threatened with 'physical elimination' by agents of the regime'," he said.

"The threats conveyed to Ms. Mohammadi make it clear that her security is at stake, unless she commits to end all public engagement within Iran, as well as any international advocacy or media appearances in support of democracy, human rights, and freedom of expression," the statement added.

The Committee said it was "deeply concerned" about the threats against Mohammadi and "all Iranian citizens with a critical voice, and call upon the authorities to safeguard not only their lives, but also their freedom of expression."

Mohammadi has been repeatedly tried and jailed for her vocal campaigning against Iran's widespread use of capital punishment and its mandatory dress code for women.

She won the Nobel primarily for her fight against the oppression of women in Iran. Her children collected the award on her behalf as she was in prison at the time.