Syria's government accused rebels of firing a chemical weapon, marking a dangerous escalation in the fight.
This is as well as protecting Syria's most sensitive sites including chemical weapon stores.
"We know the Syrian government has the capacity to carry out chemical weapon attacks, " Mr. Obama said.
In recent years, Syria transferred Scud missiles to Hezbollah, which are capable of carrying chemical weapon warheads.
"Something went down, but it was short of a chemical weapon, " a senior State Department official told CNN.
President Obama said "intelligence assessments alone are not sufficient" in guiding its assessments on chemical weapon use in Syria.
It's a person walking now with massive weapons of mass destruction into an underground, a chemical weapon or something.
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These people do not show outward symptoms of a CW (chemical weapon) attack.
But Mr Hagel and his British counterpart indicated that existing evidence of alleged chemical weapon was not sufficient to trigger an international response.
U.S. Secretary of State John Kerry told reporters in Brussels that he had spoken with Netanyahu about the assertion of chemical weapon use.
Jordan, which shares a border with Syria, is tracking reports of the attack but couldn't confirm whether it involved a chemical weapon, he said.
And a U.S. military official directly familiar with preliminary intelligence analysis of the attack told CNN there were "strong indications" that no chemical weapon was used.
On a separate issue, the spokesman said that the rebels had secured what they believe is an unexploded chemical weapon deployed by the regime Monday in Idlib.
But Professor Paul Rogers, of the University of Bradford's department of peace studies, said white phosphorus could be considered a chemical weapon if deliberately aimed at people.
This report, entitled A Report Concerning the Possible Involvement of Germans in the Establishment of a Chemical Weapon Facility in Libya, was submitted to the Bundestag on 15 February 1989.
But images posted by Syrian state-run media of the aftermath of the Aleppo incident, which the government blamed on rebels, aren't consistent with a chemical weapon attack, some observers said.
But images posted by Syrian state-run media of the aftermath of the Aleppo incident, which the government blamed on rebels, are not consistent with a chemical weapon attack, some observers said.
U.S. Defense Secretary Chuck Hagel last week said there is evidence that the chemical weapon sarin has been used on a small scale in Syria, though questions remained about the circumstances surrounding it.
As is often the case with paint jobs, the new anti-chemical-weapon paint needs an undercoat and a top coat.
During the invasion, we wore chemical protective suits because of the fear of chemical or biological weapon attack.
In unfriendly hands, these missiles could deliver a nuclear, chemical or biological weapon on the United States from anywhere on earth.
Can you say what pressure, if any, was put on intelligence analysts in the CIA, DIA, anywhere else, to endorse the view of Iraq possessing chemical and biological weapon stockpiles and reconstituting the nuclear weapons program as an imminent threat to U.S. interests?
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And because of technology today, if an organization like that got a weapon of mass destruction on its hands -- a nuclear or a chemical or a biological weapon -- and they used it in a city, whether it's in Shanghai or New York, just a few individuals could potentially kill tens of thousands of people, maybe hundreds of thousands.
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If we want to use law as a weapon against chemical weapons, we should reject the CWC and shore up the Geneva Protocol.
U.S. officials predicted before the war that at least 100 metric tons of weapon-ready chemical and biological agents would be found.
"The way Syria configured its chemical arsenal was essentially as a weapon of strategic deterrence, not really to be used on the battlefield, but as an instrument of last resort, " said Mr. Zanders of the EU Institute, likening Syria's capacity to use chemical weapons to how Israel treats its nuclear weapons.
It's okay for chemical weapons it's okay for biological weapon at the toxin and bacteriological, but not the viral.
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An October 2002 National Intelligence Estimate warned that Iraq was pursuing weapons of mass destruction, had reconstituted its nuclear weapon program and had biological and chemical weapons.
The nuclear program is his primary weapon, and that would give him the ability to use the biological and chemical better.
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