Despite rising calls for some kind of increased U.S. military involvement in Syria, scant evidence exists, at least in public, that Syria's vicious civil war has breached President Barack Obama's "red line" on the use of chemical weapons.
In the 10 days since the Obama administration notified Congress that it suspected, with "varying degrees of confidence," that chemical weapons had been employed in Syria, no concrete proof has emerged, and some headline-grabbing claims have been discredited or contested. Officials worldwide now admit that no allegations rise to the level of certainty.
Yet political rhetoric on Syria has overtaken actual evidence in a high-stakes Washington debate that's increasing pressure on Obama to lend more military support to the rebels fighting to topple Syrian President Bashar Assad.
On Monday, Senate Foreign Relations Committee Chairman Robert Menendez, D-N.J., alluded to chemical weapons as he proposed a measure that would provide limited arms to the rebels, asserting that Assad's regime "has crossed a red line that forces us to consider all options."
That assertion, however, appears far less certain than it did only a week ago. British, French and Israeli experts who expressed more confidence in their assessment than the Obama administration had in its judgment have in recent days qualified their positions, said Greg Thielmann, a former State Department intelligence analyst now with the Arms Control Association, a private organization that provides analysis of weapons issues.
"That should make everyone suspicious," he said. "And the reality may be lot more complicated."
Thielmann added, "Do you really risk going to war without knowing who has used what and in what circumstances?"
Existing evidence casts more doubt on claims of chemical weapons use than it does to help build a case that one or both sides of the conflict have employed them.
British officials now say they're uncertain how the few samples they've analyzed were gathered, handled and preserved.
The British defense secretary, Philip Hammond, told reporters in Washington last week that while that evidence led experts to suspect the use of sarin, a potent nerve gas, the samples were too degraded to be considered conclusive.
"We need hard evidence. The kind of evidence that would be admissible in court," he told a briefing of defense reporters at the British Embassy. "For that evidence to have any chance of being admitted in court, it would need to have been collected under controlled conditions, secured through a documented chain of custody to the point where it was tested. We do not yet have samples that meet that standard of evidence."
Turkish doctors over the weekend also cast doubt on another reported chemical attack, this one in the Syrian city of Saraqib, where rebels claimed some sort of chemical weapon had been dropped from helicopters.
But the doctors told the website Global Post that none of the blood they drew from alleged victims of the attack, who'd been taken to Antakya, Turkey, for treatment, tested positive for nerve gas. The samples were sent to Ankara, Turkey's capital, for additional tests.
Adding to the confusion over the weekend was Carla del Ponte, a member of the United Nations' Independent International Commission of Inquiry for Syria and a former war crimes prosecutor. Del Ponte told Swiss television on Sunday that "according to the testimonies we have gathered, the rebels have used chemical weapons, making use of sarin gas." On Monday, her Geneva-based team, which is investigating war crimes and other human rights violations in Syria, issued a statement that emphasized "that it has not reached conclusive findings as to the use of chemical weapons in Syria by any parties to the conflict."
Conclusive testing to prove or disprove chemical weapons use would require an impartial body, most likely the United Nations with the help of the Organization for the Prohibition of Chemical Weapons, to be on the ground to take soil and blood samples. Assad's regime, claiming much of the international community would not treat it fairly, has resisted the idea of a U.N. team unless it included Russian experts. Russia continues to support the Syrian regime.
Without such proof, White House spokesman Jay Carney on Monday urged caution against taking "precipitous action" based on limited evidence. He called intelligence assessments "extremely valuable, and significant," but insufficient to make a final determination on whether chemical weapons had been used.
"We are now in the process of gathering the facts, not rushing to conclusions, not acting precipitously based on an incomplete case, but gathering the facts in order to make a judgment about what policy actions the president might take in reaction to the crossing of the red line," Carney said.
Still, Carney was dismissive of Del Ponte's suggestion that it was the rebels, not the government, who had used chemical weapons, describing the White House as "highly skeptical" of the idea. A State Department official said rebels aren't believed to possess chemical weapons, and Pentagon spokesman George Little said that "if chemical weapons were used, the Syrian regime would be responsible."
"Facts are not complete, as the president himself has said, and we need to continue to gather facts and to get facts that are corroborated, and so we are doing that both through our own means and working with partners," a senior State Department official told reporters Monday, speaking on condition of anonymity to discuss the matter candidly.
David Lightman and Lesley Clark of the Washington Bureau contributed.
By Hannah Allam, Matthew Schofield and Jonathan S. Landay
McClatchy Washington Bureau