WASHINGTON -- With the United Nations preparing to investigate claims of a chemical weapons attack in northern Syria this week, the question of whether chemical weapons were used overshadows the lingering nuance of who may have used them.
It's not a small distinction. President Barack Obama has long said that Syrian government deployment of its substantial stores of chemical agents, including the nerve gases Sarin and VX, would cross a "red line," and possibly lead to military measures. The administration has also warned that failing to secure the chemicals, and letting them fall into the hands of rebels or other non-state fighters in the two-year civil war, may also prompt an American response.
The reports of a chemical weapon strike were first reported on Tuesday, when Syrian state television broadcast images of what it said were civilians struggling from a chemical dispersed after a rebel rocket strike in a government-controlled area of Aleppo. Rebel groups countered with their own videos showing victims of a rocket attack they said was launched by President Bashar al-Assad's government. About 25 people were killed. Another attack on Thursday killed at least 42 people inside a Damascus mosque.
In the Aleppo attack, witnesses and reporters described victims struggling to breathe and, in at least one instance, being overwhelmed by the smell of chlorine, a chemical sometimes mixed with explosives to enhance the effect.
The U.N. said on Thursday it would investigate the reports, a development welcomed by U.S. Ambassador to the U.N. Susan Rice, who urged full accountability from the Syrian government.
"The United States supports an investigation that pursues any and all credible allegations of the possible use of chemical weapons in Syria, and underscores the importance of launching this investigation as swiftly as possible," Rice said in a statement. "We demand the full cooperation of the Assad regime in particular, as well as Syrian authorities throughout the country, including by providing full and unfettered access to all relevant individuals and locations."
Left unsaid was that the U.N. investigation had been requested by the Syrian government.
American lawmakers sought to use the sketchy chemical weapons reports to press Obama into military action against Assad's government, without facing the murkier issue of who actually launched the attacks.
"We are extremely disturbed by reports that chemical weapons have been used today in Syria," said Sen. John McCain (R-Ariz.) and Sen. Lindsey Graham (R-S.C.) in a joint statement on Tuesday. "If today’s reports are substantiated, the President’s red line has been crossed, and we would urge him to take immediate action to impose the consequences he has promised."
Rep. Mike Rogers (R-Mich.), the chairman of the House Intelligence Committee, said in televised appearances that America was "morally obligated" to take military action against Syria's ability to deliver its chemical weapons.
"There's, at least, a high probability they have used, either in -- most recently or in the past, some amount of chemical weapons," Rogers said in a Wednesday interview on CBS. "This is the time to act. Don't wait until we have 5,000 dead. That's too late."
American officials have so far insisted they have no solid evidence that chemical weapons were deployed, although they continue to investigate.
Obama said in Israel on Wednesday that he was "deeply skeptical of any claim that, in fact, it was the opposition that used chemical weapons."
An Israeli intelligence officer told McClatchy on Thursday it was increasingly clear that some sort of chemical had been dispersed, although it was likely not any of the substances that international authorities were most concerned about, such as Sarin or mustard gas. The officer also said it remained unclear who had fired the projectile.
"It could have been the rebels, though we are very doubtful about that," the unnamed officer told the news service. “It could have been the regime, which is more likely. Or it could have been an accident. An area where chemical agents were being stored could have been bombed or improperly secured. All of these scenarios are possible, and we won’t know more until a thorough investigation is conducted."
Eliot Higgins, a British analyst who closely tracks weapons movements in Syria and was the first to notice an influx of Croatian arms into the country earlier this year, speculated that if the chlorine reports were true, it was far more likely the result of a shelling that hit a chlorine depository than a warhead carrying the chemical.
"It's really difficult to be sure, but I suspect it might be a chemical leak as a result of a rocket attack, rather than a rocket with a chemical warhead, although it's extremely difficult to be certain," wrote Higgins, who blogs under the pseudonym Brown Moses.
The Aleppo shelling appears to have taken place in a part of the city called Khan al-Assal, a mostly government-controlled area.
A rebel commander quoted in The New York Times on Thursday said he had witnessed the attack, which he said was an errant airstrike from a regime aircraft. The pro-rebel Syrian Support Group, by contrast, said an eyewitnesses had tracked a pair of Scud missiles as they were launched from a Syrian military zone near Damascus.
In what may be nothing more than coincidence, The Washington Post reported in December that rebel fighters with an extremist group called Jabhat al-Nusra apparently took control of a chlorine factory in the Aleppo area late last year, raising the possibility that the explosion had been the product of a rebel-produced dirty bomb. Last year, the State Department designated Jabhat al-Nusra as a terrorist organization in an attempt to curb its influence among rebel groups.
A pro-rebel advocacy group in Washington said in a statement on Thursday that the chemical used in the attacks in both Aleppo and Damascus had been identified as echothiophate, originally marketed as an eye drop to treat glaucoma. Echothiophate in high concentrations can simulate the effects of nerve agents, but isn't banned under the Chemical Weapons Convention.
Dan Layman, a spokesman for the Syrian Support Group, said the information on the chemical came from Free Syrian Army contacts in Damascus. He said he couldn't say how the analysis had been conducted.
Stephen L. Morgan, a professor of chemistry at the University of South Carolina who has specialized in chemical warfare, told HuffPost that identifying a chemical substance contained in a weapon would require high-tech, expensive equipment unlikely to exist in the contested areas of Aleppo.
"I can assure you that a rebel group under the conditions that they're living doesn't have the resources that they'd need to identify it," said Morgan. "In a war zone? No, not going to happen."
CORRECTION: An earlier version of this story misidentified the Syrian Support Group as the Syrian Support Network.