Coronavirus could kill as many as 3.5million Iranians if people there ignore measures aimed at preventing the spread of the bug, a study says.
Iran has reported 1,135 deaths and more than 16,000 infections as of Wednesday morning, but observers believe the situation is much worse and Tehran is underreporting its figures.
The World Health Organisation said the actual numbers could be five times higher and satellite images have shown mass graves being dug in the city of Qom.
A sobering study by Iran's Sharif University of Technology has outlined three grim scenarios which predict a catastrophic outcome for Iran, which has temporarily released prisoners, including British-Iranian mum Nazanin Zaghari-Ratcliffe, as it struggles to control Covid-19.
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In a best case scenario, about 12,000 people would die if Iranians comply with the government's preventative measures, high-risk areas are quarantined and medical supplies are sufficient.
With medium cooperation, the death toll could be as high as 110,000.
In a worst case scenario, there would be no cooperation from the public, the virus would peak in June and up to 3.5million Iranians would die, the study warned.
In that scenario, four million people would become infected.
Iran has banned non-essential travel within Iran, cancelled a traditional fire festival and urged people to stay home, but many have ignored the advice.
The Imam Reza shrine in Mashhad and the Fatima Masumeh shrine in Qom were closed to curb the spread of Covid-19.
But on Monday night, furious mobs broke through barricades stormed the sites, where worshippers normally gather at all hours to pray and kiss the shrines.
Tehran hasn't been locked down and the city's mayor, Pirouz Hanachi, said the scenario would be impossible, Deutsche Welle reported.
The mayor said: "We have neither the capacity nor the ability to put Tehran under quarantine.
"We can't take care of quarantined people. That is in part because of the [economic] sanctions."
The United States imposed fresh sanctions on Iran on Tuesday, keeping up its economic pressure campaign even as it offered to help Tehran cope with the pandemic and called on the Islamic Republic to release detained Americans.
Iran has asked the International Monetary Fund for a £4billion bailout to fight coronavirus.
On Tuesday, it temporarily freed 85,000 prisoners, including Ms Zaghari-Ratcliffe, who has been released for two weeks.
She has to wear a prison tag and can only go within 300 metres of her parents home, according to the Free Nazanin campaign.
Mrs Zaghari-Ratcliffe said she was "happy to be out, even with the ankle tag".
In a statement, she added: "Being out is so much better than being in - if you knew what hell this place is. It is mental.
"Let us hope it will be the beginning of coming home."
