Growing speculation that the Syrian regime is using chemical weapons is turning up the heat on President Barack Obama, who has warned such a move would be a game changer, AFP reports.
The US administration, both in public and in private, says it has not concluded that such arms -- of which President Bashar al-Assad's regime has a large stockpile -- have been been employed in the bloody civil war.
But "it's important that we do whatever we can to monitor, investigate and verify any credible allegations, given the enormous consequences for the Syrian people and given the President's clear statement that chemical weapons use is unacceptable," White House spokesman Jay Carney said Tuesday.
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."
Washington has also warned that any use or transfer of chemical weapons would cross a "red line" and possibly trigger military action.
Recent statements from US allies seem to suggest such arms -- illegal under international law -- may already have been unleashed.
The latest came Tuesday when Israeli Brigadier General Itai Brun, head of the research and analysis division of military intelligence, alleged Assad's regime had used chemical agents -- mostly likely sarin gas -- more than once.
"To the best of our professional understanding, the (Assad) regime has made use of deadly chemical weapons against the rebels in a number of incidents in the last few months," Brun told a security conference in Tel Aviv.
His comments come on the heels of similar assessments reported to the United Nations by France and Britain last month.
"The British and French submitted a letter to the UN Secretary General on March 21st to 'bring attention to recent allegations from various sources that chemical weapons have been used in Syria,'" a senior administration official told AFP.
Speaking on condition of anonymity, the official added that the use of chemical weapons in an environment like Syria was very difficult to confirm.
"Given the stakes involved, low confidence assessments by foreign governments cannot be the basis for US action," the official said.
US Defense Secretary Chuck Hagel, on a visit to Cairo Wednesday, said any evidence had to be weighed carefully.
"This is serious business and you want to be as sure as you can be on these kind of things," Hagel said, adding the United States ultimately had to rely "on its own intelligence."
Gregory Koblentz of the Council on Foreign Relations underscored it was important that the evidence was highly reliable, "ideally from two or more independent sources, or types of analyses that can give you that type of confidence."
And that's not currently the case in Syria, where access is tough and evidence transmission chains are weak.
"It's very difficult to make that assessment, unless you have trained experts who are on the ground immediately after an attack, or able to collect samples, interview victims, interview witnesses and move about freely," Koblentz said.
"It's not surprising to me that different countries are coming up with different assessments because the evidence isn't probably as strong and conclusive."
Aram Nerguizian of the Center for Strategic and International Studies said "it would take a lot more than a low grade assessment from the French and the British to trigger a major escalation here in Washington."
"Does that mean that there's not gonna be pressure to do something? No. There will certainly be pressure in the US, pressure in the Gulf, pressure in Syria, pressure in Europe," he told AFP.
Nerguizian also noted that Obama was cautious in formulating his warnings to Damascus, saying his statement on red lines "has always had some inbuilt ambiguity."
"An ambiguity can be an asset, and it can be a liability, if it's viewed as the ladder to something that puts the administration in a difficult position," Nerguizian said. "And it has to resist the urge for a major and uncalculated response."