Last Updated, 5:40 p.m. | As my colleagues Ben Hubbard and Hwaida Saad report from Beirut, antigovernment activists accused the Syrian government of deploying chemical weapons in a string of towns in the rebellious countryside east of the capital, Damascus, on Wednesday, killing hundreds of men, women and children.

Rebels claimed that victims of the attack, shown in dozens of video clips, were killed by chemical weapons, just days after United Nations inspectors arrived in the country to investigate previous attacks said to have involved poison gas. Syria’s government called the accusations “false and untrue” and a spokesman told the state news agency President Bashar al-Assad’s forces “will never use any weapons of mass destruction against its own people, if such weapons exist.”

While the veracity of each side’s claims could not be independently established, visual evidence uploaded to YouTube makes it clear that a large number of civilians were killed on Wednesday, including women, children and the elderly. What remained unclear was how they died, and whether they were victims of a conventional chemical agent, like sarin or mustard gas, or if their deaths might have been caused by the use of a weaker agent in a confined space.

Video shared online shows graphic images of dozens of dead people, including women and a large number of young children, including babies in diapers, most of whom were said to have suffocated. All of the video has been posted by YouTube accounts affiliated with rebels and activists in towns in the Eastern Ghouta region, including Erbeen, Kafr Batna, Saqba and Jisreen.

One clip posted on a channel affiliated with activists in Kafr Batna showed the bodies of a group of men, women and young children, including a baby in a diaper, all lying on the floor of a room. The cameraman, sobbing, said that the dead were all members of one family. Outside the room, a dimly lighted hallway was also lined with dead bodies.

Another video clip uploaded to the same channel showed a room filled with the bodies of dozens of people killed in what the cameraman called, “a new massacre in Kafr Batna.” The dead included a large number of young children. Many of the bodies are shown with their shirts lifted up to expose bare stomachs and chests, and none appear to have bled or to have sustained bodily injuries, further suggesting that suffocation was the cause of death.

Bambuser, a Web site that enables users to stream live video from their phones, posted an alert to Twitter on Wednesday that one of its users in the town of Douma posted live video of victims from the attacks in Eastern Ghouta. The graphic video shows rows of dead bodies wrapped in white shrouds.

LIVE NOW: Victims of #chemical attack in #EastGouta area, #Syria: //t.co/hFBZ4tOgGE GRAPHIC — BambuserAlert (@Bambuser_Alert) 21 Aug 13

Activists in the town of Erbeen uploaded video showing similar images: a room filled with dozens of bodies covered in sheets and blankets, slabs of melting ice balanced on their chests to fend off decomposition. The cameraman said there were more than 40 dead in the room, including a number of young boys whose bodies were in a row.

The Erbeen revels also released video that showed doctors attempting to treat children in a clinic. In the clips, one doctor pressed a manual respirator against the mouth of a boy who appeared to be nonresponsive, while a second doctor prepared to give a second child an injection. The second child appeared to barely respond, and his lips were a deep shade of blue.

Another video from Erbeen, which appears to have been filmed inside the same clinic, showed a group of doctors trying to treat a man, holding him down as his body convulsed. His eyes were closed, and the only sound he made was a series of high-pitched cries.

Rebels in the town of Jobar uploaded video of a doctor describing his experience treating many of the dead and injured Wednesday, and his description seemed to suggest that the initial assessments of chemical weapons experts may indeed be accurate. The doctor, who did not state his name, said that many of the dead hid in their basements during the attack, unaware that chemical agents are more dense than air and therefore are more concentrated and powerful in enclosed, low-lying spaces.

Opposition activists added English subtitles to a copy of the video with the doctor’s account.

“The negative thing that happened was dealing randomly with the matter and the poor education of citizens,” the doctor said. “The gas loses its effect after half an hour, but unfortunately citizens hid in basements although the gas is heavy and it comes down to basements. This increased the damages and the number of injuries. With the descending of the citizens to the basements, the number of injuries and martyrs increased.”

It is customary in the Islamic faith to bury the dead within 24 hours of their passing, and so by Wednesday afternoon many residents of Eastern Ghouta were faced with the grim task of identifying and burying the dead.

Ugarit News, an antigovernment group, posted video to YouTube that shows a woman collecting the body of a dead child, it small body covered in a white shroud and lined up in a row of bodies on the floor of a shaded outdoor patio. In shock, the woman remained silent throughout the video, while a man firmly held her upper arms and eventually lead her away.

The task of burying the dead was made harder still by the scale of the killings, and by the fact that the deaths appeared to have been caused by exposure to chemicals whose effects were both frightening and not well understood. Shams News Network, another antigovernment group, posted video to YouTube that showed at least seven victims being buried in a mass grave in the town of Erbeen. A man stood over the open pit and gave an angry sermon, holding aloft a Quran and covering his face.

In a second video posted by the same account, gravediggers shoveled dirt over the bodies of eight victims being buried together, also in Erbeen. It is not clear if both videos show the same mass grave.

A video reported produced by my colleagues at The Times looks at the debate about what kind of weapon could have caused death on the scale seen in Eastern Ghouta on Wednesday.