WASHINGTON — U.S. intelligence agencies unanimously agree that Syrians have been exposed to deadly sarin gas in recent weeks, but they are divided over how certain they can be that the Syrian regime is to blame, U.S. and congressional officials said Friday.
As the Obama administration weighs how to respond to the use of poison gas, intelligence officials say they are confident that sophisticated tests of tissue and soil samples and other evidence point to sarin. But reactions in the U.S. intelligence community have varied because of the possibility — however small — that the exposure was accidental or caused by rebel fighters or others outside the Syrian government's control, officials said.
Releases of poison gas could have occurred when soldiers loyal to the regime, which has been trying to secure and consolidate its dozens of chemical weapons sites, moved part of its stockpile, a U.S. Defense official said. Another possibility is that disloyal Syrian weapons scientists supplied chemicals to rebel fighters.
"The intel folks are taking a hard look at this, and they're not certain," the Defense official said, speaking anonymously to discuss intelligence matters. "There's no definite indication this was used against the opposition."
And the administration and its allies may never reach a clear conclusion, private experts and foreign diplomats say.
Gary Samore, who was the White House's top official on weapons of mass destruction until February, said that answering questions about the "chain of custody" would probably depend on highly sensitive intelligence that might not exist, or which the government would be reluctant to make public.
As a result, "I think there's always going to be doubt," said Samore, now with the Belfer Center at Harvard University.
After weeks of skepticism about reports that chemical weapons had been used, the Obama administration announced Thursday that the agencies making up the intelligence community had concluded "with varying degrees of confidence" that the Syrian regime had used sarin on a "small scale."
Before deciding on a response, the administration said, it wants definitive proof that the regime used the poison gas. It said it would work with the United Nations and allies such as France and Britain to find the answer.
On Friday, a top Syrian official flatly rejected any possibility of chemical weapons use.
"The U.S.-British and Western allegations in general on that issue do not have any credibility," Syrian Information Minister Omran Zoubi told Russian television during a visit to Moscow, Syria's close ally.
President Obama has declared since August that the use of chemical weapons by President Bashar Assad's regime would be a "red line," suggesting that it could trigger a military response from the United States. But administration officials, pointing to the intelligence community's blunder in declaring that Iraqi leader Saddam Hussein had weapons of mass destruction, said they needed more proof than the usual intelligence assessments.
U.S. officials haven't been willing to provide details on the attacks they have studied. But the British government, in a letter to the U.N. requesting an investigation, said it saw "limited but persuasive evidence" of chemical attacks, citing incidents March 19 and 23 in Aleppo and Damascus and an attack in Homs in December.
The British said dozens of people had been treated in Syrian hospitals for symptoms consistent with sarin exposure, including convulsions, shortness of breath and dilated pupils. They cited reports from rebels that 15 people had died in Aleppo and 10 in Damascus because of chemical attacks.
The U.S. Defense official said that at least some of the samples studied by the U.S. officials were collected in December.
The United Nations has been seeking to send a technical team into Syria since last month but has been blocked by the government, which has objected to the world body's demand for "unfettered access" to Syrian territory.
U.N. Secretary-General Ban Ki-moon has continued to press for access, and U.N. officials say they could dispatch the team within a day or two once permission was granted. But many diplomats and outside analysts think Assad may never be willing to permit access to the U.N. group because the inspectors could reach a conclusion that would unite much of the world against him.
If the U.N. team continues to be blocked, the administration will have to rely on its own intelligence assessments and that of allies, which would not be nearly as convincing to the rest of the world. Greg Thielmann, a former U.S. intelligence analyst, said the intelligence agencies' conclusions would probably be less convincing to the public because the agencies are not likely to declare that they have reached 100% certainty.
"The Iraq WMD is looming over this, as it ought to be," a senior congressional official said. "How can you be more confident in the assessment here? These are questions we are all asking."
The official noted that the agreement of all 17 intelligence agencies on sarin use contrasted with the Iraq assessments of 2002, in which the State Department's intelligence unit disagreed that Hussein had restarted his nuclear weapons program.
In the absence of overwhelming proof, obtaining U.N. Security Council support for a military response in Syria would probably prove difficult, because Russia and China are likely to be deeply resistant, diplomats say.
Samore predicted that most world opinion, including that of key European and Muslim countries, could be swayed with incomplete evidence that the Assad regime was responsible for the attacks.
He said the bigger hurdle for the United States was the lack of any attractive military options: Destroying the chemical weapons sites, which are scattered across Syria, or seizing them would require "a massive amount of force."
"The big constraint is not world opinion, but self-restraint, given how unappealing the options are," he said.
Musab abu Qatada, spokesman for a key rebel group, the Damascus Military Council, said he hoped that "the American government takes a humanitarian position and helps the targeted Syrian people regardless of political interests."
Congressional Republicans and other advocates of tough action, meanwhile, charge that the administration is intentionally setting the bar too high to avoid having to punish Assad.
Michael Singh, a former George W. Bush administration national security staffer now with the Washington Institute for Near East Policy, said the Obama administration was "unlikely to get the firm conclusion that they're looking for, which means it's not a firm red line."
Times staff writers Patrick J. McDonnell in Beirut and Raja Abdulrahim in Los Angeles contributed to this report.