Iranian Armita Gravand, 16, who has been in a coma since Sunday after what was reported as an assault by Iran's so-called morality police, is under "strict security measures" at Fajr Airforce Hospital, a human rights group told The National.
"She was physically attacked by authorities in Shohada metro station for what police perceived as non-compliance with the compulsory hijab," the Hengaw Organisation for Human Rights said.
"As a result, she sustained severe injuries and was transported to hospital."
Iran's government has denied she was attacked and said Ms Gravand fainted due to low blood pressure.
It made similar claims in September 2022 when Kurdish-Iranian Mahsa Amini died as a result of injuries believed to be sustained while she was in police custody over her dress code.
Her death sparked protests nationwide and beyond calling for the regime to be toppled.
"During the past two days, there has been no news from Armita Gravand's family," Haibat Mohammadi, of Hengaw, told The National.
"The family are under very high pressure by government officials and have been threatened against speaking to anyone, including the media, except those affiliated with the government.
"Close relatives in the hospital have had their mobile phones confiscated after a photo of Armita was leaked to the public."
Shortly after the photo was circulated on social media, Iranian authorities made Ms Gravand's parents "sit in front of state TV cameras and repeat what was dictated to them", reiterating government claims made about the reasons she ended up in a coma, Mr Mohammadi said.
"But as you can see in the picture of Armita, her head is wrapped. What do the bandages around her have to do with low blood pressure?"
"She remains in a critical condition," he added.
Hengaw has called for an "independent medical team" from Doctors Without Borders and the International Committee of the Red Cross in Tehran to independently examine Ms Gravand in the presence of a UN team, given what it called Iran's "history of withholding the truth and ongoing denial of crimes", it said, referring to Ms Amini's case.
The US has also expressed "shock and concern" over her case.
We are following news of her condition. We continue to stand with the brave people of Iran and work with the world to hold the regime accountable for its abuses," said Deputy Special Envoy for Iran Abram Paley.
Mr Paley also hit out at Tehran over the arrest of a journalist at the hospital where Ms Gravand is being treated, describing it as an "affront to journalism."
"The Iranian regime should spend more time worrying about how it treats its own people rather than how the media covers its abuses."
Speaking to The National, head of Iran studies at the Emirates Policy Centre (EPC), Mohamad Al Zghool, said while it was unclear whether Ms Gravand's case would spark a fresh round of protests, the momentum since Ms Amini's death has been ongoing.
Iranians had expected the regime would take measures to quell the public anger but instead, the government has tightened laws and heightened executions and arrests of the opposition, Mr Zghool said.
Earlier this year, Iranian supreme leader Ayatollah Ali Khamenei acknowledged that tens of thousands of people have been detained in crackdowns on protesters in recent months. Human Rights Activists in Iran, which has been tracking the demonstrations, said at least 527 people have been killed by Iranian authorities.
Other groups have criticised the regime for "sham" trials resulting in execution of political prisoners.
"Perhaps one of the most prominent features of the past decade in contemporary Iranian history is the transformation of protests from a phenomenon that repeats every decade to an annual [wave of protests] that even the Iranian regime expects every year," Mr Zghool said.
"This transformation has plunged Iranians into a continuous state of social discontent stimulated by repeated and ongoing causes, which move Iranian society and by the nature of the behaviour displayed by institutions in the face of these protests."