The gruesome discovery of what activists said were dozens of tortured corpses in Damascus, clouded efforts to end 21 months of bloodshed.
The government of President Bashar al-Assad said it welcomed any initiative for talks to end bloodshed in the country, after UN-Arab League envoy Brahimi said he had a peace plan acceptable to world powers.
The government's position, expressed by Prime Minister Wael al-Halaqi, came amid a flurry of diplomacy led by Brahimi to halt the conflict that monitors say has now killed more then 45,000 people.
Nearly 90 percent of the dead came in the past 12 months, said the UK-based Syrian Observatory for Human Rights, which relies on a network of medics and activists on the ground.
It reported the discovery of 30 tortured bodies in a flashpoint district of Damascus, while a gruesome video emerged of a separate slaying of three children in the capital.
"Thirty bodies were found in the Barzeh district. They bore signs of torture and have so far not been identified," the Observatory said.
The Syrian Revolution General Commission activist network gave a higher estimate of 50 bodies, saying "their heads were cut and disfigured to the point that it was no longer possible to identify"
The video posted online by activists showed the bodies of three young boys with their throats slit open and hands bound behind their backs.
Their bodies were discovered on Monday in Jubar.
The authenticity of the footage could not be verified.
The Observatory also reported the killing of the boys, who activists said were kidnapped the day before at a checkpoint on their way home from school.
In central Syria, the army shelled the town of Halfaya in Hama province, where an air strike on a bakery last week killed 60 people, and Houla in Homs province, where pro-regime militiamen are suspected of killing more than 100 people in May in another major massacre.
The Observatory said nearly 90 percent of the 45,000 people killed in the conflict died in 2012, putting this year's toll at 39,362 people, mostly civilians.
The uprising began in March 2011 with peaceful protests inspired by the Arab Spring but escalated into an armed rebellion following a brutal government crackdown.
The sharp increase in the death toll came in the face of an escalating resort to air power by the Assad government against densely populated areas, the Observatory said.
Although rebels now hold vast swathes of territory in both the northeast and the northwest, the government has so far stood firm despite Western predictions of its imminent fall.
"The government is working to support the national reconciliation project and will respond to any regional or international initiative that would solve the current crisis through dialogue and peaceful means and prevent foreign intervention in Syria's internal affairs,"
Halaqi told parliament.
The premier said the revolt against Assad's rule must be resolved only by the Syrian people, "without external pressures or decrees".
Halaqi said the country was "moving toward a historic moment when it will declare victory over its enemies, with the goal of positioning Syria to build a new world order that promotes national sovereignty and the concept of international law".
Brahimi said Sunday he had crafted a ceasefire plan "that could be adopted by the international community".
The proposal involved a ceasefire, the formation of a government, an election plan, and was based on an agreement world powers reached in Geneva in June.
The opposition has already rejected that accord, and insists Assad must go before any dialogue can take place.
Russia and China have so far vetoed three UN Security Council draft resolutions seeking to force Assad's hand with the threat of sanctions.
An oil embargo imposed by Syria's key EU customers has devastated its oil exports and sent the prices of staple goods spiralling.
The Syrian pound has taken a nosedive since the conflict began and was trading at 77.74 against the dollar at the official rate, compared to
55 pounds in late 2011. On the black market, the rate was 93 pounds to the dollar.