The last such analysis, released in January, documented nearly 60,000 killings through the end of November. Since then, U.N. officials had estimated higher numbers. The latest figures add more confirmed killings to the previous time period, and find almost 27,000 more between December and April.
"The constant flow of killings continues at shockingly high levels, with more than 5,000 killings documented every month since last July," said Pillay, the U.N. high commissioner for human rights. "This is most likely a minimum casualty figure. The true number of those killed is potentially much higher."
Among the victims were at least 6,561 children, including 1,729 children younger than 10.
"There are also well-documented cases of individual children being tortured and executed, and entire families including babies being massacred — which, along with this devastatingly high death toll, is a terrible reminder of just how vicious this conflict has become," Pillay said.
Her office commissioned San Francisco-based nonprofit Human Rights Data Analysis Group to study eight data sets provided by various groups containing 263,000 reported killings. Those lacking a name, date and location of death were excluded, and some duplicates were found.
The figures trace the arc of violence.
Since the start of the peaceful protests against President Bashar Assad in March 2011, which turned into an armed rebellion and then morphed into civil war, the average monthly number of documented killings has risen from around 1,000 per month in the summer of 2011 to an average of more than 5,000 per month since last July.
At its height from July to October 2012, the number of killings rose above 6,000 per month.
"Civilians are bearing the brunt of widespread, violent and often indiscriminate attacks which are devastating whole swaths of major towns and cities, as well as outlying villages," Pillay said.
"Government forces are shelling and launching aerial attacks on urban areas day in and day out, and are also using strategic missiles and cluster and thermobaric bombs. Opposition forces have also shelled residential areas, albeit using less fire-power, and there have been multiple bombings resulting in casualties in the heart of cities, especially Damascus."
The vast majority of the victims are male, but three-quarters of the reported killings do not indicate a person's age, and the analysis could not differentiate between fighters and non-combatants.
The most documented killings were in rural Damascus, with 17,800 people dead. Next were Homs, with 16,400; Aleppo, 11,900; and Idlib, 10,300.