WASHINGTON - The White House said Thursday that Syria had likely used chemical weapons against rebel forces on a "small scale," but emphasized US spy agencies were still not 100 percent sure.
US intelligence services had been investigating reports that Syrian President Bashar al-Assad's forces had used chemical arms -- a move Washington has said would cross a "red line," triggering possible military action.
US Defense Secretary Chuck Hagel first announced the assessment during a visit to Abu Dhabi, saying the "decision to reach this conclusion was made within the past 24 hours."
"Our intelligence community does assess with varying degrees of confidence that the Syrian regime has used chemical weapons on a small scale in Syria, specifically the chemical agent sarin," National Security Council spokeswoman Caitlin Hayden said.
"Given the stakes involved, and what we have learned from our own recent experience, intelligence assessments alone are not sufficient," Hayden however cautioned.
The US intelligence assessment is based "in part on physiological samples," the spokeswoman said, but she added the chain of custody was "not clear, so we cannot confirm how the exposure occurred and under what conditions."
"We do believe that any use of chemical weapons in Syria would very likely have originated with the Assad regime," a legislative aide to President Barack Obama, Miguel Rodriguez, wrote in a letter to US lawmakers.
So far, US intelligence indicates that "the Assad regime maintains custody of these weapons, and has demonstrated a willingness to escalate its horrific use of violence against the Syrian people," the letter said.
Earlier this week, an Israeli general in military intelligence alleged that Syria had used chemical agents more than once during the protracted civil war, which has left more than 70,000 people dead since it began in March 2011.
The general's comments came on the heels of similar assessments reported to the United Nations by France and Britain last month.
On March 20, during a historic visit to Israel, Obama said the use of such weapons would be a "grave and tragic" mistake on Assad's behalf and that it would be a "game changer."
If the allegations are confirmed, Obama -- who has sought to avoid any US military role in the civil war -- would face increased pressure to intervene.
Asked if the intelligence assessment meant that Syria had passed the declared "red line," Hagel said that was a policy question and that his task was to provide the US president with "options."
The use of chemical agents "violates every convention of warfare" and such arms are "uncontrollable deadly weapons" that most leaders view as being in a "different category," he added.
Hagel was speaking on the last stop of a tour of the Middle East with meetings in Israel, Jordan, Saudi Arabia, Egypt and the United Arab Emirates.
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