The number of people arrested amounts to over 10,000, the Norway-based human rights organization says.
Iran has been cut off from the outside world for over five days.
Exact figures on the number of deaths are not available, but several human rights groups in exile, as well as sources within the regime in Tehran, estimate they are in the thousands.
Some organizations, such as Iran International, estimate that over 10,000 people have been killed.
Hospitals are overwhelmed with protesters who have been shot by regime security forces, three doctors say in messages seen by the British newspaper The Guardian.
“Shooting to kill”
Many have gunshot wounds to the eyes and head, which indicates that the regime is using the same strategy as during the 2022 Iranian protest wave.
They want to damage people's heads and eyes so that they can no longer see - just like they did in 2022, says a doctor in Tehran.
The doctor describes the hospital as a war zone, where there is a shortage of both blood and equipment. There is no doubt that the shots were intentional, he says.
They shoot to kill.
Mass burial
Another doctor describes how they are treating injured protesters outdoors - in freezing temperatures - when hospitals have no room for more. One injured person is said to have had 20 bullets in his body, writes The Guardian .
On social media, numerous videos that have made it through the internet blockade, or have been smuggled out by people who have left Iran in recent days, show rows of black body bags.
On Wednesday, around 100 members of the security forces who were reportedly killed in connection with the protests will be buried, the AP news agency reports. State-run Iranian media reports that 300 dead, both civilians and security personnel, will be buried in Wednesday's mass ceremony.
