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Just days after U.N. inspectors arrived in Syria to investigate the possible use of chemical weapons, opposition activists allege that as many as 650 people have been killed in a poison gas attack. Two anti-Assad opposition groups say that a large rocket attack in Damascus on Wednesday morning was actually a chemical weapons attack launched by the regime. If the reports are confirmed, it could also be one of the deadliest single incidents of the entire war. Syria's state media agency denied the claims.

There are wildly differing reports on the casualties — from "dozens" to 213 to over 650 (and now an unthinkable 1,300) — and still no formal confirmation on the cause of death, but witnesses and reporters on the ground confirm that some kind of attack took place in the Syrian capital and that children are among the dead. Reuters reports that photographers, including their own, have taken images and videos that "showed scores of bodies including of small children, laid out on the floor of a medical clinic with no visible signs of injuries." (You can see several such images here, though you should be warned that they are very graphic and the origins are not fully confirmed.) A lack of obvious wounds would suggest that some kind of poisoning may the cause.

Reuters also quotes a nurse saying the victims "arrived with their pupils dilated, cold limbs and foam in their mouths," which are typical symbols of gas attack victims. 

Accusations of chemical weapon use have been leveled at both sides during the two-and-a-half-year conflict, but nothing has been alleged on this scale. American, British, and French sources have all claimed months ago to have found evidence that Bashar al-Assad's forces have crossed the "red line" by using nerve gas and other agents, but no international action has yet been taken against the regime, mostly because of Russia's refusal to allow a U.N. Security Council resolution.

On Sunday, United Nations inspectors arrived in the country to investigate previous claims of chemical weapon use, which makes the timing of this newest attack all the more curious. British Foreign Secretary William Hague has already asked that those same inspectors be given immediate access to the site of Wednesday's attack in order to investigate the new claims. They are staying at a Damascus hotel just a few miles from where the attack reportedly took place.

UPDATE: The U.S. and France have joined Britain in calls for a U.N. investigation of the crash site, and have convened a Security Council meeting for 3:00 p.m. on Tuesday. Russia (which has veto power of the Security Council) has already suggested that the attack may have been perpetrated by the rebels as a provocation, meant to be blamed on the government, dashing any hopes of significant movement at the U.N.

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