The camera pans up from three blindfolded men with their hands bound to a rebel fighter speaking into a megaphone. He stands by a white pickup truck, his face covered with a white and red checkered scarf.

In classical Arabic, the man reads out the death sentence of the three men. It lasts one minute and 45 seconds before the man proclaims "God is great" and two of his comrades - wearing black ski masks - fire single bullets into each of the three captives' heads. As they slump over, a crowd erupts in cheers and celebratory gunfire.

In the two years since the war in Syria started, there have been innumerable videos of summary executions, beheadings and the aftermath of massacres. But in recent days, the videos posted online from Syria have highlighted a deepening sectarianism and a brutality never before seen in this conflict.

The execution of the three men, who were officers of the Syrian government, took place in a public square in Raqqa, a northern city controlled by the Sunni, al Qaeda-linked extremist rebel group, Islamic State of Iraq and al-Sham. The slain men were Alawites, the sect of Shia Islam that President Bashar al-Assad and his most loyal forces belong to.

"We respond to the criminal Bashar who is killing Sunnis everywhere," the man with the megaphone said. "Now we decided to come close to God by killing those Alawites…"

The speaker in the Raqqa video said the executions were in revenge for - among other things - recent massacres in and around the majority Alawite coastal city of Baniyas in early May. There, regime forces are reported to have carried out "cleansing" operations of Sunni areas, slaughtering hundreds of men, women and children. Videos showed rows of dead bodies, shot or stabbed, as well as the charred remains of bodies burned in a building. Many more remain missing, feared dead.

"The fear of ethnic cleansing has increased among all populations of Syria and with good reason," writes Syria analyst Joshua Landis at the University of Oklahoma. "Sunnis claim today that the regime is effectively trying to clear many areas of its Sunni inhabitants."

"If Assad reasserts his control over rebel held parts of Syria, large populations of Sunnis would likewise flee," Landis continues. "They would fear ruthless retribution and possible massacres."

The Raqqa public execution clip surfaced just days after another grisly video was posted online of a Sunni rebel commander slicing open the body of a dead regime soldier with a knife, removing his lung and biting into it. "I swear to God we will eat your hearts and your livers, you soldiers of Bashar the dog," the man says to the camera.

"Hopefully we will slaughter all of them [Alawites]," the commander, Khalid al-Hamad, later told TIME Magazine, which first uncovered the clip. "I have another video clip that I will send to them. In the clip, I am sawing another shabiha [pro-government militiaman] with a saw. The saw we use to cut trees. I sawed him into small pieces and large ones."

As the world reacted with horror, the main political Syrian opposition group, the Syrian National Coalition, condemned the action and called for the man to be tried. The military wing, the Free Syrian Army said it "completely rejects the ill-treatment of the wounded and the disfigurement of the dead."

"It is not enough for Syria's opposition to condemn such behavior or blame it on violence by the government," said Nadim Houry, the Middle East deputy director of Human Rights Watch. "The opposition forces need to act firmly to stop such abuses."

The clips have come to light as the U.S. and its allies continue to grapple with the question of arming the rebel forces, worried that any weapons could end up in the hands of extremists. Videos like that of the rebel eating the organs of his enemy have compounded those fears since he is part of what the West considers to be the more mainstream rebel forces, those that would theoretically receive any arms.

Syrian opposition leaders blame the West for the rise in sectarianism and extremists rebel groups like Jabhat al-Nusra which are among the most ferocious groups fighting Assad forces. It could have been stopped, they say, if the more moderate forces had been supported earlier.

Both the execution and "cannibal" videos rocketed around the internet, creating a firestorm on social networking sites. Opposition activists argue they are isolated incidents not representative of the rebel forces fighting the Assad regime, while supporters of Assad argued that their true character is finally coming to light.

On both sides, many fear the sectarianism is now so deep-seated that Syria will never be able to recover from it.

"Two yrs ago, there was no such thing as decapitation, massacre & cannibalism in Syria," wrote one Assad supporter on Twitter. "Today these barbaric acts are synonymous to the country."

ABC News' Nasser Atta contributed to this report