More than 60,000 people have been killed in Syria since the uprising against President Bashar al-Assad's regime erupted in March 2011, the UN High Commissioner for Human Rights has said.
Navi Pillay said that an exhaustive analysis carried out by data specialists showed that 59,648 people had died through to the end of November.
"The number of casualties is much higher than we expected, and is truly shocking," she said.
The majority of those killed were males, Pillay added.
Speaking to Al Jazeera, Rupert Colville, spokesman for Pillay, said the death toll could be much higher.
"What we have done is take the statistical analysis of seven of the lists of casualties that exist, analyse them all and remove all the double counting," he said.
"But the criteria are quite strict. There has to be a set amount of information and there may well be people who have been killed who aren't included as a result of that."
Colville said the 60,000 figure "should be treated as an indicative number and not a real number". "It is probably the minimum," he said.
'Work in progress'
Pillay had said in January 2012 that the UN was unable to provide a precise figure on the number of deaths.
In-depth coverage of escalating violence across Syria
"We have not been able to verify the circumstances of each and every death, partly because of the nature of the conflict and partly because we have not been allowed inside Syria since the unrest began in March 2011," Pillay said.
She added that "once there is peace in Syria, further investigations will be necessary to discover precisely how many people have died, and in what circumstances, and who was responsible for all the crimes that have been committed".
The analysis - which Pillay stressed is "a work in progress, not a final product" - shows a steady increase in the average number of documented deaths per month since the beginning of the conflict, from around 1,000 per month in the summer of 2011 to an average of more than 5,000 per month since July 2012.
The greatest number of reported killings have occurred in Homs (12,560), rural Damascus (10,862) and Idlib (7,686), followed by Aleppo (6,188), Daraa (6,034) and Hama (5,080), the analysis found.
"This massive loss of life could have been avoided if the Syrian government had chosen to take a different path than one of ruthless suppression of what were initially peaceful and legitimate protests by unarmed civilians," Pillay said.
"As the situation has continued to degenerate, increasing numbers have also been killed by anti-government armed groups, and there has been a proliferation of serious crimes including war crimes, and - most probably - crimes against humanity, by both sides."
Pillay also criticised the international community for failing to do more to stop the crisis, saying: "Collectively, we have fiddled at the edges while Syria burns."
Her comments came as activists reported on Wednesday the deaths and injury of dozens of people in an airstrike on a petrol station in the suburbs of Damascus.