Warning: This article contains graphic descriptions of death and injury

Heading home after joining a protest in Tehran on 8 January, Reza put his arms around his wife Maryam to protect her. "Suddenly, I felt my arm go light – there was only her jacket in my hands," he told a family member, who later spoke to BBC Persian. Maryam had been fatally shot - and they had no idea where the bullet had come from.

Reza carried Maryam's body for an hour and a half. Exhausted, he sat down in an alley. After a short time, the door of a nearby house opened. The people who lived there took them into their garage, brought a white sheet and wrapped Maryam's body in it.

Days before Maryam headed out to the protests, she had told her children - aged seven and 14 – about what was happening in their country. "Sometimes parents go to the protests and don't come back," she said. "My blood, and yours, is no more precious than anyone else's."

Reza and Maryam's names have been changed for safety reasons.

Maryam is one of thousands of protesters who should have returned home but never did, as the authorities responded to the rapid spread of demonstrations across Iran with a deadly crackdown.

The US-based Iranian Human Rights Activists News Agency (HRANA) says it has been able to confirm the killing of at least 2,400 protesters, including 12 children, during the past three weeks.

It is extremely difficult to determine the death toll, which is expected to rise in the coming days, because the country remains under a near-total internet blackout imposed by Iranian authorities on Thursday night.

Human-rights groups have no direct access to the country and, along with other international news organisations, the BBC is unable to report on the ground.

Iranian authorities have not provided a death toll but local media have reported 100 security personnel have been killed, and protesters - whom they have portrayed as "rioters and terrorists" - have set fire to dozens of mosques and banks in various cities.

Demonstrations began in the capital, Tehran, on 29 December, following a sharp fall in the value of the Iranian currency against the dollar. As the protests reached dozens of other towns and cities, they turned against Iran's clerical rulers.

Security forces soon launched a violent crackdown, with at least 34 protesters reported killed by 7 January, the 11th day of the unrest. However, it appears the bloodiest crackdown was last Thursday and Friday, when thousands of people took to the streets across the country and called for an end to the rule of the Supreme Leader, Ayatollah Ali Khamenei.

BBC Persian has received dozens of accounts from inside Iran. Defiant despite potential repercussions, the witnesses said they wanted to ensure the rest of the world knew of the violence against the protesters.

"Our neighbourhood smells of blood - they killed so many," one told BBC Persian. Another recalled security forces "mostly shooting at heads and faces".

The protests have spread across all 31 provinces. And the information trickling in clearly shows the scale of the killings in smaller cities and towns is just as severe as in major cities.

In Tonekabon, a town of 50,000 people in the north, Sorena Golgun was killed on Friday. The 18-year-old university student was "shot in the heart" running from an ambush by security forces, according to a family member.

Like Sorena, many of the other protesters killed were young and full of dreams. Robina Aminian, a 23-year-old fashion-design student who hoped to study in Milan, was shot dead in Tehran on Thursday.

Her mother spent about six hours travelling from their home, in the western city of Kermanshah, to collect Robina's body from Tehran. On her way back, she held her beloved daughter in her arms. But when she arrived, the security forces made her bury the body in a remote cemetery outside the city - with no other family or friends present.

Not all those killed were protesters. Navid Salehi, a 24-year-old nurse in Kermanshah, was shot multiple times leaving work on Thursday.

The bodies of many protesters were sent to the Kahrizak Forensic Medical Centre, in Tehran.

The scenes there were so distressing Sahanand, who did not want to give his real name, decided to travel almost 1,000km to a border area so he could send out video footage by using the mobile data networks of neighbouring countries. On Saturday, Sahanand had seen more than 2,000 bodies lying on the ground, he said.

Again, the BBC has no means to confirm this. However, in two newly emerged videos from Kahrizak, BBC Verify and BBC Persian have counted at least 186 bodies in one piece of footage and at least 178 bodies in the other. The two videos probably show some of the same bodies, so we cannot be definitive, but the true figure is likely to be much higher.

One young woman, speaking to BBC Persian on condition of anonymity, described last week's events as like "a war". The protesters remained "more united than ever before" but it was too much for her and this week she had fled the country - like many, gripped by fear the authorities will start a new wave of executions and prosecutions.

"I'm really afraid of what might happen to those who are still in Iran," she added.

Additional reporting by Farzad Seifikaran and Hasan Solhjou