Doctors Without Borders says some 355 people who showed "neurotoxic symptoms" died following the suspected chemical weapons attack this week near Syria's capital.
The Paris-based humanitarian aid group said Saturday that three hospitals it supports in the Damascus region reported receiving roughly 3,600 patients who showed such symptoms over less than three hours on Wednesday morning.
A debate has ensued about who was behind the alleged gas attack on rebel-held Damascus suburbs that activists previously said killed more than 130 people. The attack has spurred demands for an independent investigation and renewed talk of potential international military action, if chemical weapons were indeed used.
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The organization released a statement Saturday describing symptoms including convulsions, extreme salivation, contracted pupils and sight and respiratory problems.
The charity said many were treated with atropine, a drug administered to those with "neurotoxic symptoms."
"[We] can neither scientifically confirm the cause of these symptoms nor establish who is responsible for the attack," said the organization's Director of Operations Bart Janssens.
"However, the reported symptoms of the patients, in addition to the epidemiological pattern of the events, characterized by the massive influx of patients in a short period of time, the origin of the patients, and the contamination of medical and first aid workers, strongly indicate mass exposure to a neurotoxic agent."
Anti-government activists accuse the Syrian government of carrying out the toxic gas attack on the eastern suburbs of Damascus and have reported death tolls ranging from 136 to 1,300.
Government points finger at rebels
Syrian Deputy Prime Minister Qadri Jamil said foreign militants carried out the attack with the backing of Israel and supporters in the West in a bid to thwart efforts to hold an international peace conference to end the Syrian bloodshed.
"We can only say that extremist forces carried it out, linked to foreign forces, since no Syrian can do this against another Syrian," he said Wednesday. "At the head of these forces are those who have promoted vengeance and hatred and spoke of ousting the regime by force over the past two years."
Canada's Foreign Affairs Minister John Baird said this week that evidence of a possible chemical weapons attack was mounting, but he stopped short of confirming a chemical attack actually took place.
"The fact that Syria continues to bombard this specific geographic area ... is telling," Baird said at a press conference Friday afternoon. “The fact that Syria will not let the UN inspectors who are on the ground in the country today visit this area is a very telling action.”
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Baird said he has met with his British counterpart, William Hague, and both of them are “troubled” by the United Nations Security Council’s inability to take decisive action.
Wednesday's attack came as a UN team was on the ground in Syria investigating earlier claims of chemical weapons attacks.
More than 100,000 people have been killed in Syria during more than two years of clashes between forces loyal to Syrian President Bashar al-Assad and opposition fighters seeking to overthrow his regime.