RENEE MONTAGNE, HOST:
It's MORNING EDITION, from NPR News. I'm Renee Montagne.
STEVE INSKEEP, HOST:
And I'm Steve Inskeep. Here's the problem faced by President Obama's administration: When the United States says it's going to do something, it will face pressure to actually do it.
MONTAGNE: President Obama warned Syria not to cross the red line of using chemical weapons. The language suggested some strong response would follow. And now even the U.S. agrees with its allies in charging that Syria's government has used chemical weapons in a civil war.
INSKEEP: But before responding, the administration is expressing doubts about its own finding and seeking more proof. Here's NPR's Larry Abramson.
LARRY ABRAMSON, BYLINE: The announcement came just days after Britain, France and Israel all said they had indications Syria might have used chemical weapons. At first, U.S. officials seemed wary of these assertions. Then, on Thursday, Secretary of Defense Chuck Hagel took to the microphones in Abu Dhabi, where he is ending a weeklong tour of the Middle East.
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SECRETARY CHUCK HAGEL: The U.S. intelligence community assesses with some degree of varying confidence that the Syrian regime has used chemical weapons on a small scale in Syria, specifically the chemical agent sarin.
ABRAMSON: That seems like a bold statement, but it's actually full of caveats. Note that Hagel says varying confidence. U.S. officials have indicated that intelligence agencies are not all in total agreement on the finding. One said the case is a strong maybe. Hagel said there are more unknowns than there are hard facts.
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HAGEL: We still have some uncertainties about what kind of chemical was used, where it was used, who used it.
ABRAMSON: The administration says part of the intelligence assessment is based on physiological samples, like human tissue, for example. That sort of evidence suggests the U.S. has been able to examine something from the scene of an alleged attack. Syrian opposition groups say they have been trying to send tissue samples from alleged victims for analysis here.
But the administration would not say whether it was relying on those kinds of samples. And even tissue samples might not prove the case, according to Chris Bidwell of the Federation of American Scientists.
CHRIS BIDWELL: It would not be enough to base a finding on, because you don't really know how it got there, what the chain of custody was, how many people handled it, touched it, altered it, possibly.
ABRAMSON: As Bidwell notes, Syrian opposition groups have a vested interest in showing that chemical weapons have been used, since that might spark U.S. intervention. And what sparked the U.S. decision to suddenly announce this finding? The administration says it was reached only in the last 24 hours or so, and was a response to members of Congress.
Senator John McCain has long advocated a more aggressive U.S. role in the conflict. And he said the announcement shows the Syrian regime has crossed the line the administration laid out, and the U.S. must take appropriate steps.
REPRESENTATIVE JOHN MCCAIN: Provide a safe area for the opposition to operate, establish a no-fly zone, and provide weapons to the people in the resistance who we trust.
ABRAMSON: But the administration gave no indication it's ready to change course. The Pentagon remains concerned that Syria's formidable air defenses would make it tough to establish a no-fly zone. And there's concern that arms supplied to the rebels could end up helping terrorists also fighting there. The administration would only say more proof is needed, and backed a U.N. effort to investigate. But so far, Syrian resistance has stymied a U.N. effort to take a first-hand look. Larry Abramson, NPR News, Washington. Transcript provided by NPR, Copyright NPR.