French surgeon Jacques Beres told a meeting of human rights activists the carnage in Syria was among the most horrific he had witnessed 40 years operating in war zones.
Dr Beres smuggled himself into the battered Syrian city of Homs for two weeks in February, setting up a makeshift hospital in a home where he operated on 89 wounded people in 12 days, many of them elderly or children. He saved most of them, but nine died on the operating table.
At yesterday's meeting in Geneva, Switzerland, the 71-year-old Parisian - apparently the only Western doctor to get into Homs - spoke with passion about the bloodshed and the horrific conditions.
"This is a hell," said Dr Beres, a co-founder of Doctors Without Borders and Doctors of the World who has worked in war zones including Vietnam, Rwanda and Iraq. "It's mass murder. It's totally unfair. It's unjustifiable."
Dr Beres went to Syria at the request of two groups, France-Syrie Democracy and the Union of Muslim Associations in France. He crossed the border illegally from Lebanon to set up his operating table in an abandoned home with just three beds.
He said his biggest challenges were the basics: scarce electricity and finding enough room for stretchers.
Dr Beres said that people in Homs, the heart of the Syrian rebellion, lived in despair despite their gratitude to journalists for telling the world of their plight.
"They say it's good that you're thinking about us, but they say it doesn't give us food, medicine or weapons," he told the Geneva Summit for Human Rights and Democracy.
The Syrian uprising began in March with mostly peaceful protests in a number of the country's impoverished provinces. As security forces violently suppressed them, killing thousands, the protests grew and escalated into an armed insurrection.
The United Nations refugee agency said 230,000 Syrians had fled their homes since the uprising against Assad's regime began last year. The UN says more than 7,500 people have been killed in the past 12 months and activist groups say the death toll for the 11-month-old uprising has surpassed 8,000.
Hadeel Kouki, a 20-year-old Syrian activist, told the group she spent 52 days in prison after the Syrian military intelligence summoned her for questioning for handing out leaflets at her university, urging fellow students to demonstrate.
"We have about 10,000 dead until now and the killing is constant. We have about 100 dead every day. This number includes a lot of children. They die in their homes," said Ms Kouki, who studied English literature and law.
She said the first time she was arrested, she spent 40 days in prison under "horrible circumstances" and then was arrested twice more. The authorities, she said, "tortured me with electricity and abused me in very bad ways in prison".
She said she was released but denied the right to return to university at Aleppo. She is now in Egypt, engaged in cyber activism against Syrian president Bashar Assad.
The Assad regime insists that it is fighting foreign terrorists and criminal gangs, denying that the year-long uprising is a popular revolt.
But Ms Kouki said there were no foreign fighters in Syria.
"I can tell you all of that is not true," she said. "There were no foreigners, there were no terrorists. That's propaganda of the government."