Haroon Siddique, at The Guardian, reports: My colleague Ian Sample, has been speaking to chemical weapons experts who say the videos appear to show signs of poisoning but doubt whether there will be an opportunity to independently verify what happened and also questioned the timing of the alleged attacks.

One chemical weapons inspector who is not in Syria told the Guardian:

I very much doubt the team will be given access to the site. The whole inspection has been delayed for weeks and months already over the formalities of visiting each site.

That could change if the pressure becomes so huge for the Syrian government that they have to let them in, but if an attack has happened as appears that would be a PR catastrophe. With an incident of this size, the team will try to talk to the Syrians. If the government thinks this hasn’t happened, the inspectors can say they should want proof, so why not give them access.

Unconfirmed videos of the aftermath of the attack show dead children and adults, and others with a range of symptoms, including constricted pupils, difficulty breathing, foaming at the mouth, and shaking or fits. These are consistent with a sarin attack, but are not enough to confirm that a nerve agent was responsible.

Ralph Trapp, an expert on chemical and biological weapons, said:

It is possible a gas was involved, but the images I’ve seen were not clear enough to see other symptoms beyond difficulty in breathing and suffocation. It certainly looks like some sort of poisoning.

Many symptoms can be caused by other substances, and chemical weapons inspectors will need to rule these out. Missiles can strike chemical stores, realising poisonous gases like chlorine, which is used to sterilise water. Shells that carry sarin can also carry fuel-air explosives, which can cause people to suffocate. The munition produces a huge cloud of fuel that is ignited to produce a blast and suck huge amounts of oxygen out of the air.

Though the videos are almost impossible to verify, Trapp said the footage shows what a chemical weapons attack on a civilian area would look like.

This is one of the first videos I’ve seen from Syria where the numbers start to make sense. If you have a gas attack you would expect large numbers of people, children and adults, to be affected, particularly if it’s in a built up area.

Scott Lucas reports: Only hours after the mass killing of civilians in airstrikes by the Assad regime — possibly using chemical weapons — news has broken that the US military has ruled out American intervention, even of a limited nature, in Syria.

In a letter sent on Monday to Congressman Eliot Engel, the Chairman of the Joint Chiefs of Staff, General Martin Dempsey, said the American military is capable of taking out the Syrian air force and shifting the balance of the civil war.

However, Dempsey argued that the approach would plunge the US into another war in the Arab world and offer no strategy for peace, given the fragmented opposition to the Assad regime:

Syria today is not about choosing between two sides but rather about choosing one among many sides. It is my belief that the side we choose must be ready to promote their interests and ours when the balance shifts in their favor. Today, they are not.

Dempsey, who was recently in Israel for discussions, said Syria’s war was “tragic and complex”:

It is a deeply rooted, long-term conflict among multiple factions, and violent struggles for power will continue after Assad’s rule ends. We should evaluate the effectiveness of limited military options in this context.

Dempsey said that US should concentrate on increased humanitarian assistance to bolster a “moderate” opposition as “the best framework for an effective US strategy toward Syria”.