Human Rights Watch has called on the UN Security Council to impose sanction on Syria and to hold the government accountable to the International Criminal Court, following the deaths of more than 800 people in recent weeks.
The organisation released a report on Thursday based on interviews with victims and witnesses.
The report strongly suggests that the systematic killings and torture qualify as crimes against humanity.
According to witnesses, many people were left with lethal head, neck and chest wounds. Civilians were deliberately targeted by security forces who used lethal force against protesters and bystanders, in most cases without warning.
"For more than two months now, Syrian security forces have been killing and torturing their own people with complete impunity," said Sarah Leah Whitson, Middle East director at Human Rights Watch. "They need to stop - and if they don't, it is the Security Council's responsibility to make sure that the people responsible face justice."
The protests first broke out in Daraa in response to the detention and torture of 15 children accused of painting graffiti slogans calling for the government's downfall. In response and since then, security forces have repeatedly and systematically opened fire on overwhelmingly peaceful demonstrators.
Nine witnesses from the towns of Tafas, Tseel, and Sahem al-Golan described an attack which took place on April 29, when thousands of people from towns surrounding Daraa attempted to break the blockade on the city. Witnesses said that the security forces stopped the protesters who were trying to approach Daraa at a checkpoint near the Western entrance of Daraa city.
One of the witnesses from the town of Tseel who participated in the protest said: "We stopped there, waiting for more people to arrive. We held olive branches, and posters saying we want to bring food and water to Daraa. We had canisters with water and food parcels with us. Eventually thousands of people gathered on the road - the crowd stretched for some six kilometers. Then we started moving closer to the checkpoint. We shouted "peaceful, peaceful," and in response they opened fire. Security forces were everywhere, in the fields nearby, on a water tank behind the checkpoint, on the roof of a nearby factory, and in the trees, and the fire came from all sides. People started running, falling, trying to carry the wounded away. Nine people from Tseel were wounded there and one of them died."