Further information in the White House summary included details on prior "small scale" use of chemical weapons by the Assad regime, as well as specifics on how Syrian forces planned, coordinated and executed the multiple strikes in and around Damascus.
National security officials began briefing lawmakers on Assad's chemical stockpiles in August and have been keeping Congress up to date on the program since then, according to a second administration official.
"This is not a new program," the official said of Assad's chemical weapons program.
"It is vast. It is extensive and very well run" the official told reporters.
White House officials also indicated that U.S. intelligence had picked up signs that Syrian forces were taking efforts to conceal the attacks from United Nations inspectors.
Details from various human sources and communications intercepts showed "a level of concern of detection and attribution" of the attacks that would point to "a commanded operation" to release the chemical ordnance orders, the first official said.
The details of the attack and its aftermath were "fully vetted" by all members of the intelligence community, up to and including Director of National Intelligence James Clapper, the official added.
Secretary of State John Kerry said Friday that the intelligence findings on the Syrian attacks are “as clear as they are compelling.”
“I'm not asking you to take my word for it. Read for yourself, everyone, those listening, all of you, read for yourselves the evidence from thousands of sources, evidence that is already publicly available,” Kerry said.
While both officials declined to comment on specific collection methods or intelligence operations by the United States in Syria, recent revelations on those classified activities were published by The Washington Post.
Specifics of U.S.-led intel operations in Syria were included in a raft of secret documents leaked to the Post by former intelligence contractor Edward Snowden.
The administration’s 178-page summary of its 2014 budget request for the 16 agencies that make up the intelligence community also provides an assessment of the agencies’ successes, failures and primary objectives, the Post reported on Thursday.
On Syria, the documents showed the National Security Agency (NSA) had set up various "listening posts" inside Syria to monitor radio and other electronic communications, known as signals intelligence, by Assad's forces at the beginning of the country's civil war.
The National Reconnaissance Office (NRO) also reportedly collected signals intelligence from sensors planted near suspected chemical weapons sites in Syria, as well as in other countries, the Post reported.
Like the NRO, the NSA agents also routinely use sensors and other collection devices, planted on the ground in hostile countries, to intercept and monitor communications that do not pass through the Internet.
One joint program with CIA, known as "CLANSIG," is a covert intelligence program designed to track radio and telephone communications in "hostile territory," according to documents obtained by the Post.
The CIA invested more than $1.7 billion in fiscal 2013 alone to finance "technical collection" efforts around the world, including programs like CLANSIG and others run by the NSA, the NRO and other intelligence organizations.