What kind that response would take, Obama is still deciding on it in consultations with his national security team, White House Press Secretary Jay Carney told reporters at his daily news conference.
The White House, however, made clear that the objective of a response from the US is not to change regime in the troubled country.
"When the President has an announcement to make, he'll make it," Carney said.
"There is no doubt here that chemical weapons were used on a massive scale on August 21 outside of Damascus," he said.
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"There is also very little doubt, and should be no doubt for anyone who approaches this logically, that the regime of President Bashar al-Assad is responsible for the use of chemical weapons. We have established with a high degree of confidence that the Syrian regime has used chemical weapons already in this conflict," Carney said.
"So the deliberations that are taking place now and the options that are being considered by the President and his national security team are not around the question of whether or not chemical weapons were used in Syria on a significant scale, causing mass death and injury to innocent civilians, to women and children.
Carney said the US is signatory to a global chemical weapons convention opposing the use of such weapons. He said there must be a response if any country violates the convention.
"They are about responding to clear violation of an international standard that prohibits the use of chemical weapons. We are also very much engaged in an effort to support the opposition in its struggle with the Assad regime as the Assad regime continues to try to massacre its own people in an effort to maintain power," he said.