Washington: The American intelligence community has assessed with "varying degrees of confidence" that the Syrian regime has used chemical weapons on a small scale, specifically the chemical agent sarin, the White House said on Thursday.
In identical letters to Senators Carl Levin and John McCain, the White House said its assessment is based in part on physiological samples, adding, "The US intelligence community assesses with some degree of varying confidence that the Syrian regime has used chemical weapons on a small scale."
"Our standard of evidence must build on these intelligence assessments as we seek to establish credible and corroborated facts. For example, the chain of custody is not clear, so we cannot confirm how the exposure occurred and under what conditions," said Miguel E Rodriguez, Assistant to the US President and Director, Office of Legislative Affairs.
"Precisely because the President takes this issue so seriously, we have an obligation to fully investigate any and all evidence of chemical weapons use within Syria. That is why we are currently pressing for a comprehensive United Nations investigation that can credibly evaluate the evidence and establish what took place," said the letter dated April 25, a copy of which was obtained by PTI.
US Defence Secretary Chuck Hagel also went public to allege that the US has evidence that the Assad regime has used chemical weapons in Syria.
"We are also working with our friends and allies, and the Syrian opposition, to procure, share and evaluate additional information associated with reports of the use of chemical weapons so that we can establish the facts," the White House letter said in response to a question asked by the senators a day earlier.
"Given the stakes involved, and what we have learned from our own recent experience, intelligence assessments alone are not sufficient - only credible and corroborated facts that provide us with some degree of certainty will guide our decision-making and strengthen our leadership of the international community," the White House official said.
Noting that the US and the international community have a number of potential responses available, the official said no option is off the table.
A day earlier, Senators John McCain, Carl Levin, Bob Corker, Robert Menendez, Saxby Chambliss, Bob Casey, Lindsey Graham and Kelly Ayotte in a letter urged US President Barack Obama to answer the question of whether the Assad regime - or Syrian elements associated with, or supported by the regime - have used chemical weapons in Syria since the current conflict began in March 2011.
Senator Bob Corker, termed it as "deeply troubling."
Corker was among a bipartisan group of senators yesterday who sent the letter to the President asking for an unclassified answer.
"This assessment is deeply troubling, and if correct, means that President Obama`s redline has certainly been crossed. While more work needs to be done to fully verify this assessment like making sure we understand the chain of custody of the evidence, it is becoming increasingly clear that we must step up our efforts," Corker said.
"I should make clear, however, that if it comes to the use of military force, before the president takes any action to commit US forces to any effort in Syria or elsewhere, I expect him to fully consult with the Senate and seek an authorisation for the use of military force," he said.