The number of people killed in Syria following a crackdown on protesters since March has reached at least 4,000, the UN rights chief said on Thursday.
"We are placing the figure at 4,000. But the information coming to us is that it's much more," said United Nations High Commissioner for Human Rights Navi Pillay during a conference in Geneva.
Pillay will address a special session of the Human Rights Council on Friday called to discuss the findings of an independent panel on the human rights situation in Syria.
The Indepedent Commission of Inquiry said on Monday Syrian forces had committed crimes against humanity, including the murder and torture of children, following orders from the highest levels of Bashar al-Assad's regime.
The panel gathered evidence from 233 witnesses and victims on the brutal repression of anti-regime protesters but was not given permission to enter the country.
A previous toll issued by the UN earlier this month put the number of estimated deaths at 3,500.
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Pillay gave the revised figure, which she described as "conservative", during questions posed by journalists at the launch of a social media campaign promoting Human Rights Day on December 10.
Asked if the situation in Syria met the criteria of an armed conflict, Pillay said it would be necessary to study the report to see the extent of action by opposition forces.
"I have said that as soon as there were more and more defectors threatening to take up arms -- I said this in August to the Security Council -- that there's going to be a civil war," the High Commissioner said.
"It's a question of studying the report to see the extent of what they call the opposition forces in order to reach the characterisation of armed conflict."
European Union foreign affairs chief Catherine Ashton led calls on Monday for the special Human Rights Council session following the publication of the report.
A draft EU resolution condemns the "serious systematic violations of human rights" committed by Syrian authorities and asks that the findings be submitted to the UN General Assembly and the UN Security Council.
The Human Rights Council previously held special sessions on Syria on April 29 and on August 22-23.