US says Syria likely to have used chemical weapons
The United States says it has "varying degrees of confidence" that Syria has used chemical weapons against rebel forces.
US intelligence services have been investigating reports that Syrian president Bashar al-Assad's forces used chemical arms - a move Washington has said would cross a "red line", triggering possible military action.
Earlier this week a senior Israeli general said he believed the Assad regime had used sarin poison gas "a number of times", citing as evidence photos of victims with contracted pupils and foam coming out of their mouths after an incident in March.
Now the US says there is evidence that chemical weapons have been used "on a small scale".
"Our intelligence community does assess with varying degrees of confidence that the Syrian regime has used chemical weapons on a small scale in Syria," US National Security Council spokeswoman Caitlin Hayden said.
The assessment, which she said was based in part on "physiological samples", points to the possible use of sarin, a man-made nerve agent.
Sarin gas was used in terrorist attacks in Japan in 1994 and 1995, and possibly during the Iran-Iraq war in the 1980s.
Immediate signs of exposure are a runny nose, shrunken pupils and blurred vision, leading to convulsions, respiratory failure and death.
Ms Hayden warned the chain of custody of the weapons was "not clear, so we cannot confirm how the exposure occurred and under what conditions".
"Given the stakes involved, and what we have learned from our own recent experience, intelligence assessments alone are not sufficient," she said.
We do believe that any use of chemical weapons in Syria would very likely have originated with the Assad regime.Chuck Hagel
US defence secretary Chuck Hagel, speaking in Abu Dhabi, said the decision to release the intelligence report had been "made within the past 24 hours" and warned that use of such weapons "violates every convention of warfare".
"We cannot confirm the origin of these weapons, but we do believe that any use of chemical weapons in Syria would very likely have originated with the Assad regime," he said.
A US defence official travelling with Mr Hagel confirmed that the phrase "varying degrees of confidence" is a term commonly used by the intelligence community to indicate disagreement among various agencies.
But the assessment reflected a degree of certainty that Syria most likely has fired chemical agents and was not merely a tentative suspicion, the official said.
In London, Britain's Foreign Office too said it had "limited but persuasive" evidence of the use of chemical agents in Syria's grinding civil war, which the UN says has left more than 70,000 people dead since it began in March 2011.
Mounting evidence of chemical weapons attacks on fighters battling Assad's regime could increase the pressure on US president Barack Obama - who has sought to avoid any US military role in the conflict - to intervene.
"All options are on the table, in terms of our response, and it could run a broad spectrum of activity across our various types of efforts in Syria," a senior White House official said, adding that Washington was consulting with its allies.
The Obama administration laid out the intelligence assessment in a letter to US lawmakers from Miguel Rodriguez, director of the White House office of legislative affairs.
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.
Last month, during a historic visit to Israel, Mr Obama said the use of chemical weapons would be a "grave and tragic" mistake on Mr Assad's behalf and that it would be a "game changer".
Asked if the intelligence assessment meant that Syria had passed the declared "red line", Mr Hagel said that was a policy question and that his task was to provide the US president with "options".
Chemical weapons are "uncontrollable deadly weapons" that most leaders view as being in a "different category", Mr Hagel said at the end of a Middle East tour of Israel, Jordan, Saudi Arabia, Egypt and the United Arab Emirates.
The Pentagon has already sent more than 200 troops to Jordan, including a US Army headquarters element, to prepare for a possible joint operation with allies to secure chemical weapons.
"I think it's pretty obvious that a red line has been crossed," said senior US Senator John McCain, adding that the key now was to ensure chemical weapons did not fall into the wrong hands.
"Some of them are in heavily contested areas and could easily fall into the hands of jihadist extremists," he told CNN.