As Western powers try to verify claims that the Syrian government used chemical weapons this week in a northeastern suburb of Damascus, the Syrian government is accusing rebel forces of doing the same.
State-run television reported Saturday that Syrian armed forces had surrounded Jobar, the opposition-held district on the edge of Damascus that saw some of the 1,300 reported dead in Wednesday's early morning attack. Several of the soldiers were "suffocating" from exposure to gases as they entered the city, according to state TV.
"It is believed that the terrorists have used chemical weapons in the area," Syrian TV reporting, citing anonymous source. The government uses the term "terrorists" to describe rebel forces.
It showed video of a room containing gas masks and gas canisters that the Army said were discovered in a storage facility in Jobar. CNN could not independently confirm the veracity of the claims or the authenticity of the video.
Opposition leaders deny involvement in the attack, which they say killed hundreds near the capital.
The competing claims surfaced as a White House official told CNN that President Barack Obama was meeting with his national security team to discuss the alleged chemical weapons attack
"Once we ascertain the facts, the president will make an informed decision about how to respond," the official said on condition of anonymity. "We have a range of options available, and we are going to act very deliberately so that we're making decisions consistent with our national interest as well as our assessment of what can advance our objectives in Syria."
In an exclusive interview with CNN that aired Friday, Obama said the United States and United Nations inspectors were gathering information on the attack, but that preliminary signs pointed to a "big event of grave concern."
"It is very troublesome," he said. "That starts getting to some core national interests that the United States has, both in terms of us making sure that weapons of mass destruction are not proliferating, as well as needing to protect our allies, our bases in the region."
The Syrian government has steadfastly denied its forces used chemical weapons outside Damascus or elsewhere.
"We said it from the first moment and, here, we assure again that we have never used chemical weapons (around Jobar) or any other region in any form whatsoever -- ... liquid, gas or whatever," Information Minister Omran al-Zoubi said Saturday in an interview with a private Lebanese channel.
Al-Zoubi went on to say that, on the contrary, his government is "quite certain that (the rebels) are the ones using chemical weapons."
The opposition, though, has a Rebel different view. Syrian National Coalition Secretary-General Badr Jamous said Friday that rockets -- some with chemical warheads and others conventional weapons -- had been fired into a heavily populated civilian area.
Most of the more than 1,300 reported dead were killed by chemical weapons, said Khaled al-Saleh, a spokesman for the umbrella opposition group.
Al-Saleh said that medical teams in the affected area had administered 25,000 shots of atropine -- a medication used to treat people exposed to the nerve gas sarin -- after the attack.
Video showed rows of bodies without apparent injury, as well as people suffering convulsions or apparently struggling to breathe.
CNN could not verify where or when the videos were recorded, and could not confirm the number of casualties.
Adding weight to the assertions that chemical weapons were used was a statement Saturday by Medecins Sans Frontieres, also known as Doctors Without Borders.
Three hospitals -- all supported by the international organization -- in Syria's Damascus governorate reported having received some 3,600 patients displaying neurotoxic symptoms last Wednesday morning, the statement said.
Of them, 355 reportedly died, it said.
"Medical staff working in these facilities provided detailed information to MSF doctors regarding large numbers of patients arriving with symptoms including convulsions, excess saliva, pinpoint pupils, blurred vision and respiratory distress," said Dr. Bart Janssens, MSF director of operations.
Patients were treated using atropine.
"MSF can neither scientifically confirm the cause of these symptoms nor establish who is responsible for the attack," said 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."
How will the world respond?
On Saturday, world leaders weighed their options.