WARNING: Graphic images

Scores of bodies, all with their hands bound behind their backs and apparently shot in the head, were discovered washed up in a river that runs through the middle of the city of Aleppo in the north of Syria on Tuesday. It is not immediately established who carried out the executions, but rebel forces and the regime of President Bashar al-Assad each accused the other.

The Syrian Observatory for Human Rights, an activist organization based in Britain with a network of contacts in Syria, said at least 65 bodies had been located, scattered along the banks of a small river in the Bustan al-Qasr neighborhood, which is mostly under rebel control, the New York Times reported. Later reports put the tally higher.

A Free Syrian Army fighter at the scene told Al-Jazeera said many more bodies were still being dragged from the water in a rebel-held area.

"Until now, we have recovered 68 bodies, some of them just teens," Capt. Abu Sada said, adding that all of them had been "executed by the regime."

"But there must be more than 100. There are still many in the water, and we are trying to recover them."

Syria’s state news agency, SANA, later posted a report on its Web site that blamed the insurgent Islamist fighters of the Nusra Front, labeled a terrorist group by the United States, and said the killings added to “a series of brutal massacres perpetrated by the terrorist groups against unarmed civilians.”

Meanwhile Tuesday, Lakhdar Brahimi told the U.N. Security Council the conflict has reached "unprecedented levels of horror," the BBC reported.

The U.N.-Arab League envoy said Syria was being destroyed "bit by bit" with grave consequences for the wider region.

"Unprecedented levels of horror have been reached. The tragedy does not have an end," Brahimi told a closed meeting of the 15-member council, diplomats told the BBC.

"The country is breaking up before everyone's eyes. Only the international community can help and first and foremost the Security Council."

Speaking later to reporters, Brahimi said the Syrian government and the opposition were, between them, destroying Syria "bit by bit."

"The region is being pushed into a situation that is extremely bad," he said.

"That is why I believe the Security Council simply cannot continue to say: 'We are in disagreement, therefore, let's wait for better times.' I think they have to grapple with this problem now."

The 22-month conflict has claimed more than 60,000 lives and created approximately 2 million internally displaced people, and more than 700,000 people have fled as refugees to Jordan, Turkey, Lebanon, Iraq and Egypt, according to UNHCR.