A member of U.N. investigation team takes samples of sands near a part of… (Associated Press )
WASHINGTON -- The United States now has evidence that sarin gas was used in the chemical weapons attack against innocent Syrian civilians, Secretary of State John F. Kerry said Sunday.
The new evidence adds to the case that the Obama administration will make to Congress for taking military action against Bashar Assad's regime, one that they are confident lawmakers will heed, Kerry said.
"I don't believe that my former colleagues in the United States Senate and the House will turn their backs on all of our interests, on the credibility of our country, on the norm with respect to the enforcement of the prohibition against the use of chemical weapons," Kerry said on NBC's "Meet the Press," one of several interviews he was to sit for less than 24 hours after President Obama's surprise decision to seek a congressional vote on a military strike against the Syrian government.
Kerry said that hair and blood samples on first responders in East Damascus "tested positive for signatures of sarin," information that just came to light "in the last 24 hours."
DOCUMENT: U.S. chemical weapons intel
"We are saying that the high confidence that the intelligence community has expressed and the case that I laid out the other day is growing stronger by the day. We know where this attack came from. We know exactly where it went. We know what happened exactly afterwards," he said. "I think this is a very powerful case and the president is confident that as that case is presented to the United States Congress and the American people, people will recognize that the world cannot stand aside and allow an Assad or anybody else to break an almost 100-year-old acceptance. These weapons are not to be used."
The news adds to the responsibility on lawmakers, Kerry said, to uphold U.S. obligations under the Chemical Weapons Convention and the Syria Accountability Act that were passed by Congress.
"Iran will read importantly what we decide to do with respect to the enforcement of this convention in Syria. Likewise, Israel. Israel is at risk, Jordan is at risk, Turkey is at risk, the region is at risk, and we believe that the Congress of the United States will do what is responsible," he said.
On "Fox News Sunday," Kerry said that "people should be celebrating" Obama's decision to seek a congressional mandate, which strengthens the American hand against Syria.
PHOTOS: Syria before the war
"The Assad regime is already on the defensive. They are being significantly impacted by the potential of these strikes. We do not lose anything, we actually gain," he said. "What we gain is the legitimacy of the full-throated response of the Congress of the United States and the president acting together."
Asked if the president would go ahead with a strike in the event of a vote against authorizing force, Kerry said he "can't contemplate" the Congress doing so, arguing it would be tantamount to Congress having "granted impunity to a ruthless dictator to continue to gas his people."
"Those are the stakes, and I don't believe the Congress will do that," he said on Fox.
Some members of Congress will return to Washington on Sunday for the first time since the start of the August recess for a classified briefing at the Capitol. The Senate Foreign Relations Committee will hold the public hearing on Tuesday to consider the administration's request to authorize force.
The House is not scheduled to return until Sept. 9, though many lawmakers in both parties are pressing the leadership to call members back sooner.
[For the record, 8:18 a.m. Sept. 1: An earlier version of this post incorrectly quoted Kerry as speaking of "the Congress of the United States and the Congress acting together." The correct quotation is "the Congress of the United States and the president acting together."]