"I think the best bet for Syria now is to keep Assad as leader," wimcorbijn wrote. "It is the right time for (countries such as Brazil, Russia, India, China and South Africa) to step in and support to help to defeat the rebels. Once the rebels are defeated, they can force to introduce democracy as well as political reforms in Syria."

Air attacks, shelling, tank fire, bomb attacks, street-to-street fighting and sectarian fighting have all contributed to the rising toll, Pillay said. Deaths have increased from 1,000 a month in the summer of 2011 to more than 5,000 a month since July, she said.

Deaths have been most prevalent in Homs, the Damascus outskirts, Idlib, Aleppo, Daraa and Hama. More than three-quarters of the victims are male, and 7.5% are female, Pillay said. The gender of the others isn't clear, and analysts couldn't "differentiate clearly between combatants and non-combatants."

The inability of the U.N. Security Council and the international community to stop the violence "shames us all," she said.

Death estimates have varied among opposition groups that have issued daily counts. For example, the Syrian Observatory for Human Rights says more than 46,000 people have died since March 2011.

U.N. data specialists counted 59,648 people reported killed in Syria between March 15, 2011, and November 30, 2012, Pillay said. Scores of deaths were reported every day in December.

Latest clashes

On Wednesday, fighting sent the daily death toll higher. More than 207 people were killed, mostly in and around Damascus, according the opposition Local Coordination Committees of Syria.

Syrian government warplanes hammered the Damascus suburbs and other targets. At least 74 people died and dozens were wounded in the Damascus suburb of Mleiha when government planes carried out an airstrike on a fuel station, the LCC said, citing initial reports. The toll of "martyrs" will probably rise "due to continuous pulling of the bodies from under the rubble," the LCC said.

Aerial shelling also was reported in the Damascus suburb of Harasta, in the cities of Aleppo and Deir Ezzor and other locations.

In Idlib province, Syrian rebels, including jihadists, fought to wrest a key military air base from government forces Wednesday, the opposition said, as anti-regime fighters kept up the heat on al-Assad's forces. Al-Nusra Front, a militant group that the United States designated last month as a terrorist movement, is among three rebel factions attacking the base, rebels said in a statement.

"The battle to liberate Taftanaz military airport has started," the rebels said. "Taftanaz airport has been delivering horrors to Muslims. The warplanes fly from there on a daily basis, to throw explosive barrels on villages and towns."

The other factions participating in the effort are Battalions of Ahrar Al-shaam and the Islamic Forefront. Ahrar is an Islamist coalition with some Salafist elements that cooperates with the Free Syrian Army. The Islamic Forefront is a larger umbrella group of Islamist organizations; one of its members is Ahrar.

About 400 soldiers are based at the airport, along with a number of pro-government militia.

At the base are 30 planes, including transportation craft and fighting jets; seven armored vehicles, including tanks and armored personnel carriers; artillery and rocket launchers.

Casualties have been reported on both sides in the fighting, but precise numbers were not available because the government has restricted international journalists' access.