Five months of analysis have led UN-backed researchers at Benetech, a non-profit technology firm, to conclude that 59,648 individuals have been killed in Syria between the start of the rebellion on March 15, 2011, and November 30, 2012.

"Given there has been no let-up in the conflict since the end of November, we can assume that more than 60,000 people have been killed by the beginning of 2013," Pillay said. "The number of casualties is much higher than we expected and is truly shocking."

This is the first estimate from the United Nations since May, when UN Secretary General Ban Ki-Moon said the death toll stood at around 10,000.

The study also reflected an increase in the monthly death tolls, which had averaged about 1,000 per month in the summer of 2011 and soared to more than 5,000 per month, on average, since July 2012.

Civilians killed in bombing

News of the study's findings came out Wednesday, amid activist reports of a government airstrike near Damascus. The Syrian Observatory for Human Rights reported a fatal attack on a service station in the suburb of Maliha, saying "dozens" were killed or injured.

Maliha is one of the Sunni Muslim suburbs around the Syrian capital that have been bombarded by President Bashar Assad's troops. Government forces control the center of Damascus and are hitting the suburbs through air attacks in an attempt to quash the rebellion.

In another attack in the Damascus suburb of Maadamiyet al-Sham, the London-based Observatory said, a family of at least 12 people died Wednesday as Syrian troops shelled the area.

Rebels have been increasingly fighting Assad's troops in and around the capital in an effort to overthrow the regime.

Rebels on the offensive

The rebel fighters intensified their attacks on Wednesday as well, targeting a military airport in the northern province of Idlib.

The rebels, some from Islamist units lined to al Qaeda, targeted the Afis military airport near Taftanaz air base, trying to cripple some of Assad's air defenses by firing on helicopters with machine guns and mortars.

tm/msh (dpa, Reuters)