The Syria war has reached "unprecedented levels of horror", UN envoy Lakhdar Brahimi said after dozens of men were killed in a grim new massacre.
Brahimi told the divided UN Security Council that it must now act to halt the carnage epitomized by the nearly 80 young men killed with a single bullet and dumped in a river in the battlefront city of Aleppo.
Syrian rebels blamed President Bashar al-Assad's government for the killings, but state media said an Islamist opposition faction was to blame.
Syria "is breaking up before everyone's eyes. Only the international community can help, and first and foremost the Security Council," Brahimi told the council's 15 ambassadors, apologizing for sounding like a "broken old record."
Kuwait Wednesday kicked off an international donors conference for civilians caught up in the Syrian conflict with a pledge of $300 million, as UN chief Ban Ki-moon warned of a "catastrophic" situation.
"Due to the great sufferings of the Syrian people and to help ensure the success of the conference, I announce the Kuwaiti donation of $300 million for the Syrian people," Kuwait Emir Sheikh Sabah al-Ahmad al-Sabah said as he opened the one-day conference in Kuwait City.
Also addressing the International Humanitarian Pledging Conference for Syria, Ban called for urgent financial aid, warning that if funds were not forthcoming "more Syrians will die."
"The situation in Syria is catastrophic," the UN chief said as he urged all parties to the conflict to "stop the killings".
The United Nations says that more than 60,000 people have been killed in Syria's 22-month conflict, which erupted in March 2011 with peaceful protests but morphed into an armed insurgency after a harsh regime crackdown.
"The tragedy does not have an end," Brahimi said.
The Assad government's legitimacy has been "irreparably damaged," Brahimi said, however warning that it could still cling to power.
Assad's forces have become more repressive, the former Algerian foreign minister was quoted as saying in the closed meeting, but he added that both the state and the rebel opposition were committing "equally atrocious crimes."
He also warned of growing conflict "contamination" in neighboring countries.
"Most regional parties have aligned with one of the parties in Syria," Brahimi said.
"Syria is becoming a playground for competing forces," he declared. "None of the neighbors is immune to the fallout consequences of the conflict."
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The Security Council has been paralyzed on Syria for more than a year. Russia and China have vetoed three western-drafted resolutions which would simply have threatened sanctions.
Russia accuses the West of seeking regime change through force and insists it cannot make Assad stand down. The United States and its allies back the opposition stance that there can be no talks with Assad.
Brahimi went from the meeting to dinner with the ambassadors of the five permanent council members -- including Russia and the United States -- but US ambassador Susan Rice said "the same issues that have stymied the council to date remain unresolved, so there is no obvious way forward."
In Aleppo, rebel fighter Abu Seif said 78 bodies had been retrieved from the Quweiq River and that 30 more were still in the water but could not be reached because of the threat of Assad snipers.
Hundreds of distressed people watched as muddied corpses were dredged from the Quweiq.
"The regime threw them into the river so that they would arrive in an area under our control, so the people would think we killed them," Abu Seif said.
A government security official blamed "terrorists" -- the regime term for the rebels -- for the carnage.
There was no immediate claim of responsibility, but the official SANA news agency said the jihadist Al-Nusra Front carried out the executions.
Al-Nusra, which has gained notoriety for its suicide bombings, has become a key fighting force, leading rebel attacks throughout the embattled country.
Its suspected affiliation to the Al-Qaeda offshoot in Iraq have seen it added to the US list of terrorist organizations.
"My brother disappeared weeks ago when he was crossing the regime-held zone, and we don't know where he is or what became of him," said Mohammed Abdel Aziz.
Volunteers heaped bodies on a truck. They were then taken to a school where they were laid out and covered.
"We do not know who they are. They were not carrying papers," one volunteer said as bodies were taken to a local school.
On the eve of the donors' conference in Kuwait, US President Barack Obama announced an extra $155 million to aid refugees fleeing what he said was "barbarism" propagated by Assad's government.
Charity organizations pledged $182 million (136 million euros) for Syrians.
Kuwaiti press reports say the Gulf state's emir, Sheikh Sabah al-Ahmad al-Sabah, would announce a pledge of $500 million at the meeting to be attended by UN Secretary General Ban Ki-moon.