"Given there has been no letup 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," U.N. High Commissioner for Human Rights Navi Pillay said in a statement. "The number of casualties is much higher than we expected, and is truly shocking," she added.
"The failure of the international community, in particular the Security Council, to take concrete actions to stop the blood-letting, shames us all," Pillay said. "Collectively, we have fiddled at the edges while Syria burns."
A regime airstrike on a gas station in a Damascus suburb on Wednesday pushed that death toll in the civil war even higher. Anti-government activists said dozens were killed and wounded when the strike ignited an inferno and left behind a gruesome trail of charred bodies. It may be one of the bloodiest attacks in weeks.
Mohammed Saeed, an activist who visited the site in the eastern suburb of Mleiha, said the missile struck as drivers waited in line with their cars at the station. Syria is facing a fuel crisis and people often wait in line for hours to get gas.
An amateur video posted online showed the carnage at the scene, where black smoke billowed from the fire.
In northern Syria, rebels clashed with government troops near at least three airports, part of their push to cut into the government's air power.
A number of rebel groups, including the Islamic extremist Jabhat al-Nusra, attacked a helicopter base near the village of Taftanaz in Idlib province. Videos posted online showed them blasting at targets inside the airport with heavy machine guns mounted on the backs of pick-up trucks.
The videos appeared to be genuine and corresponded to other AP reporting on the issue.
Rebels also clashed with government forces near the Mannagh airport in Aleppo province and near the Aleppo international airport, shutting down air traffic for a second straight day, activists said.
In another blow to the regime and Syria's economy, a Philippine-based container port operator says it has pulled out of Syria and withdrawn all of its Filipino workers from a key port because of the civil war.
The move by Manila-based International Container Terminal Services Inc., through its Syrian subsidiary Tartous International Container Terminal, could effectively derail cargo services in the northwest port city of Tartus, Syria's largest port.
The family of American journalist James Foley revealed Wednesday that he had been missing in Syria for more than one month. He was providing Agence France-Press with videos and his family said he was kidnapped by unknown gunmen on Thanksgiving day.
The family called on those holding him to contact them.
"James is a professional journalist who has remained totally neutral in this conflict," AFP chairman Emmanuel Hoog said in a statement. "His captors, whoever they may be, must release him immediately."
Covering Syria has been a challenge for journalists. The government rarely gives visas to journalists, prompting some to sneak in with the rebels, often at great danger to themselves.
The new U.N. analysis said monthly casualty figures have been steadily increasing since the conflict began in March 2011.
Independent experts compared 147,349 killings reported by seven different sources — including the government — for the study, which was commissioned by the U.N. human rights office.
By removing duplicates they arrived at a list of 59,648 individuals killed between the start of the uprising on March 15, 2011, and Nov. 30, 2012. In each case, the victim's first and last name, the date and the location of his or her death were known.
The real death toll is likely to be even greater because reports containing incomplete information were excluded and a significant number of killings may not have been documented at all by the sources available.
"There are many names not on the list for people who were quietly shot in the woods," Pillay's spokesman Rupert Colville told The Associated Press.
The data, which didn't distinguish among soldiers, rebels and civilians, also show that the killing in Syria has accelerated.
During the summer of 2011, shortly after the uprising against Assad began, the monthly death toll stood at around 1,000. A year later, an average of 5,000 were killed each month, the U.N. said.
Most of the killings occurred in Homs, followed by rural Damascus, Idlib, Aleppo, Daraa and Hama. At least three quarters of the victims were male.
The U.N. rights chief warned that thousands more would die or suffer terrible injuries if the conflict continues, and repeated her call that those responsible for the killings — which in some cases could amount to war crimes — should be held accountable.
"We must not compound the existing disaster by failing to prepare for the inevitable — and very dangerous — instability that will occur when the conflict ends," she said.
"Serious planning needs to get under way immediately, not just to provide humanitarian aid to all those who need it, but to protect all Syrian citizens from extra-judicial reprisals and acts of revenge" like those seen in Afghanistan, Iraq, Somalia and Congo, she said.
The U.N. refugee agency said about 84,000 fled Syria in December alone, bringing the total number of refugees from the conflict about a half million. Many more are displaced inside Syria.