Top White House officials tell CNN the president called lawmakers Thursday night to say the administration has no doubt President Bashar al-Assad's regime in Syria is behind deadly chemical attacks.
Though CNN's Frederick Pleitgen reports the Syrian defense minister recently sent a letter to the defense minister of Iran saying the rebels are the ones responsible for the attacks in the country.
Secretaries of State, Defense and others, refute this claim and assured the group the U.S. has intercepted communications "from a high level Syrian official which clearly indicates they were responsible for these weapons."
One key GOP senator, Bob Corker, emerged from the briefings to announce support for what he called "surgical, proportional military strikes given the strong evidence of the Assad regime's continued use of chemical warfare."
Democratic Senate foreign relations chair Bob Menendez reaffirmed his support too, saying "a decisive and consequential U.S. response is justified and warranted."
Others argued the president still has to come before congress and the American people before he acts.
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The White House could release evidence the Syrian government used chemical weapons on its own people as early as Thursday, CNN's Barbara Starr reports.
In an interview with PBS Newshour, the President left no doubt who the U.S. believes ordered the chemical weapons attacks, saying:
"We want the Assad regime to understand that by using chemical weapons on a large scale against your own people – against women, against infants, against children, that you are not only breaking international norms and standards of decency, but you're also creating a situation where U.S. national interests are affected, and that needs to stop."
Among the evidence proving the Syrian regime's hand behind chemical weapons use: intercepts of Syrian commanders discussing the movement of chemical weapons to the area of the attack, provided by Israeli intelligence.
The U.S.'s potential next step, launching cruise missile strikes, has put the U.S. at direct odds with Russia.
"We do not believe the Syrian regime should be able to hide behind the fact that the Russians continue to block action on Syria at the U.N., State Department Deputy Spokesperson Marie Harf tells the press.
"But behind the scenes officials are signalling the U.S. may not wait for the U.N. to act," Starr says.
"The U.S. military is strengthening its position in the Eastern Mediterrrean with the addition of two more submarines."
The Syrian regime is also getting prepared.
Bashar al-Jaafari, Syria's ambassador to the UN, says "We are in a state of war right now preparing ourselves for the worst scenario."
But the rhetoric from the Syrian government has also become more subdued now.
"You can tell that the regime is getting more and more nervous," reports CNN's Frederik Pleitgen.
Pleitgen says many Syrians are also getting fearful and trying to leave the country now.
“People seem unsure what the future will bring with the American air strikes looming.”