The U.S. intelligence community had indications the Bashar al-Assad regime was preparing to launch a chemical weapons strike on an opposition-controlled area outside of Damascus in the days leading up to the attack, according to an intelligence assessment released by the White House on Friday.
"In the three days prior to the attack, we collected streams of human, signals and geospatial intelligence that reveal regime activities that we assess were associated with preparations for a chemical weapons attack," the assessment read.
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The report found that "Syrian chemical weapons personnel" were deployed outside of Damascus in an area that the regime uses for its sarin gas operations, in the three days leading up to the attack. It also disclosed that the regime had prepared for the attack with gas masks.
A senior administration official told reporters that the United States has used private channels to try to dissuade the Syrian regime from using chemical weapons in the past, but did not indicate whether it tried this strategy in the days leading up to the August attack.
"We have actually pursued diplomatic efforts to forestall the use of chemical weapons, at various junctures over the past year when we saw particularly concerning things," said the official. "That includes by the way direct communication to the Syrian government as well."
Another official said the administration might not have been able to prevent the attack from taking place because of timing.
"Timelines for all of our streams of intelligence are different," said the official. "In some cases we can and do get something close to real time, and other times because of the nature to the access … there is some built-in delay."
The White House’s determination that Assad was behind the attack is based on signal and geospatial intelligence. It estimated casualties at 1,429, including at least 426 children.
Administration officials described Assad’s chemical weapons operation as "tightly commanded and tightly controlled," adding that operatives are heavily vetted. They said Assad’s prior use of chemical weapons, as well as the trajectory of the missiles used in the attack, were also indicative of the regime’s involvement.
One official said the motivation was the "frustration [Assad’s forces] had with the opposition control of these suburbs," and their interest in securing the area in preparation for a major push toward Aleppo.
President Barack Obama has been "consulting" with Congress and international allies, but has yet to decide on his course of action, according to the administration.
"Ultimately [the president] will make the decision that is in the best interest of the United States on his own timeline," said the official.
In a speech on Friday, Secretary of State John Kerry made the case for a military response to Assad.
"Fatigue does not absolve us of our responsibility," said Kerry. "Just longing for peace does not necessarily bring it about."