The United Nations’ human rights chief said Wednesday that more than 60,000 people have been killed in the bloody conflict in Syria, a figure that far exceeds even estimates given by opposition groups after nearly two years of fighting.

“The number of casualties is much higher than we expected and is truly shocking,” U.N. Human Rights Commissioner Navanethem Pillay said, according to Reuters news service.

The tally, which Pillay said was based on an “exhaustive” five-month analysis in which researchers cross-referenced seven sources, shows 59,648 people killed between March 15, 2011, and Nov. 30, 2012. It does not specify whether the dead were rebels, soldiers or civilians.

Given that the conflict has not eased since the end of November, Pillay added, “we can assume that more than 60,000 people have been killed by the beginning of 2013.”

The Syrian Observatory for Human Rights, a group based in Britain that keeps a running tally of fatalities in Syria, said last week that approximately 45,000 people have been killed in the conflict.

A look at the Syrian uprising nearly two years later. Thousands of Syrians have died and President Bashar al-Assad remains in power, despite numerous calls by the international community for him to step down.

The U.N. figures came on a day when the Syrian military was accused of carrying out an airstrike on a gas station on the outskirts of Damascus that killed up to 70 people, according to the opposition Local Coordination Committees network.

A graphic video of the attack in Mleiha posted online shows several cars and trucks on fire and spewing black smoke as one man holds a dismembered body and screams, “God is great!” Charred bodies also can be seen amid the raging fire.

Men dig through twisted beams and rubble at the site, looking for survivors. At one point, a dazed man with blood streaming down his face climbs out of the wreckage.

Despite recent efforts by Lakhdar Brahimi, the joint U.N.-Arab League envoy to Syria, to revive the political process and bring the warring parties to the negotiating table, there appears to be little chance for a truce at the moment.

Brahimi was in Moscow for talks with officials last weekend but did not appear to win any substantive concessions from the Russian government on how to deal with the crisis.

Russian Foreign Minister Sergei Lavrov invited Mouaz al-Khatib, president of the Syrian Opposition Coalition, to travel to Moscow for talks but was rebuffed. Khatib also demanded that the Russian government apologize for its support of Syrian President Bashar al-Assad.

Heavy fighting broke out Wednesday between rebel forces and the Syrian military at the Taftanaz military airport in Idlib province. Rebel fighters have targeted the facility, saying they are seeking to prevent air attacks on civilians in the area.

Timeline: Major events in Syria’s tumultuous uprising that began in March 2011.

An opposition spokesman in Idlib province who uses the nom de guerre Abu Khalid al-Idlibi said that several extremist religious groups are taking part in the battle in Idlib, including Ahrar al-Sham and the al-Nusra Front, a group that the State Department has labeled a foreign terrorist organization with links to al-Qaeda in Iraq. The al-Nusra Front has proved to be one of the most successful rebel groups in the fight against Assad’s forces.

“The mujaheddin are now at the fences of the airport trying to enter,” Idlibi said in a Skype interview, using the Arabic term for holy warriors. “There is fierce resistance.”

Suzan Haidamous and Ahmed Ramadan contributed to this report.