U.S. intelligence officials and outside experts are looking into claims of a new and massive chemical weapons attack that's left hundreds dead. From the limited evidence they've seen so far, those reports appear to be accurate. And that would make the strike on the East Ghouta region, just east of Damascus, the biggest chemical weapons attack in decades.

The early analysis is based on preliminary reports, photography and video evidence, and conclusions are prone to change if and when direct access to the victims is granted. Over the past nine months, the Syrian opposition has alleged dozens of times that the Assad regime has attacked them with nerve agents. Only a handful of those accusations have been confirmed; several have fallen away under close scrutiny. But Wednesday's strike, which local opposition groups say killed an estimated 1,300 people, may be different.

"No doubt it's a chemical release of some variety -- and a military release of some variety," said Gwyn Winfield, the editor of CRBNe World, the trade journal of the unconventional weapons community.

While the Obama administration says it has conclusive proof that the Assad regime has used chemical weapons in the recent past, the White House has been reluctant to take major action in response to those relatively small-scale attacks. ("As long as they keep body count at a certain level, we won't do anything," an American intelligence official told Foreign Policy earlier this week.) But this attack appears to be anything but small-scale. If allegations about this latest attack prove to be accurate,  the strike could be the moment when the Assad regime finally crossed the international community's "red line," and triggered outside invention in the civil war that has killed over a hundred thousand people.

Videos and pictures allegedly taken from the Ghouta incident show young victims who are barely able to breathe and, in some cases, twitching. Close-up photos show their pupils are severely constricted. All of these are classic signs of exposure to a nerve agent like sarin. And sarin is the Assad regime's chemical weapon of choice.

"There's no smoking gun here, but it's all consistent with nerve gas exposure," a U.S. intelligence official told The Cable. "This video is consistent with all of the other ones where we believe it [chemical weapons use] actually happened."