White House spokesman Jay Carney told reporters Friday that the U.S. continues to investigate evidence that the Syrian government has used chemical weapons in its fight against rebels, but he resisted setting a timetable for possible action.
“It has been assessed by our intelligence community with varying degrees of confidence that the Syrian regime has used chemical weapons on a small scale in Syria, specifically the chemical agent sarin," Carney said. "Now we are working to establish credible and corroborated facts to build on this intelligence assessment in order to establish a definitive judgment as to whether or not the president's red line has been crossed.”
Top-ranking lawmakers on both sides of the aisle declared Thursday that the "red line" in Syria had been crossed, calling for "strong" U.S. and international intervention after administration officials revealed that the intelligence community thinks chemical weapons were used.
Sen. Dianne Feinstein, D-Calif., chairwoman of the Senate intelligence committee, and Sen. John McCain, R-Ariz., were among those urging swift action.
McCain, who has long called for more involvement in Syria, voiced concern that the administration would use "caveats" to avoid acting on the new intelligence. He said America's enemies are paying "close attention" to whether the U.S. follows through, as the White House signaled it wanted to see more proof before responding to the new information.
"I worry that the president and the administration will use these caveats as an excuse not to act right away or act at all," McCain told Fox News. "The president clearly stated that it was a red line and that it couldn't be crossed without the United States taking vigorous action."
He called for the U.S. to help establish a no-fly zone and "safe zone" in Syria, as well as provide weapons to the "right people."
Defense Secretary Chuck Hagel first revealed the intelligence assessment, which was detailed in a letter to select members of Congress, while speaking to reporters on a visit to Abu Dhabi. The administration then released those letters, which said U.S. intelligence determined with varying degrees of confidence that "the Syrian regime has used chemical weapons on a small scale in Syria, specifically the chemical agent sarin."
Secretary of State John Kerry further confirmed that there were two documented instances of chemical weapons use.
The White House, however, stressed that this was not enough to confirm how the nerve gas was released -- though acknowledged it is "very likely" to have originated with the regime of Bashar Assad -- and pressed the United Nations for a "comprehensive" investigation. The letter from the White House director of the Office of Legislative Affairs to leading members of the Senate Armed Services Committee said the assessment was based in part on "physiological samples."
A White House official also urged caution, invoking the Iraq war as an example of why the administration should be absolutely certain before going forward.
"Given our own history with intelligence assessments, including intelligence assessments related to WMD, it's very important that we are able to establish this with certainty and that we are able to provide information that is airtight ... to underpin all of our decision-making," the official said. "That is, I think, the threshold that is demanded given how serious this issue is."
A senior U.S. defense official told Fox News the Defense Department has been preparing a wide range of contingency plans for military involvement in Syria for the past year. President Obama has seen the plans and is fully aware of those options.
The options, according to this official, range from establishing no-fly zones to creating humanitarian zones to launching strikes on chemical weapons sites, select regime leadership and other targets. The official emphasized that no decisions have been made about whether to further involve the U.S. military in Syria and that there are still many questions that need to be answered first.
A United Nations spokesman said the chemical weapon findings reinforce the need for U.N. officials to "be given the requested swift and unfettered access to Syria that it needs to determine whether chemical weapons have indeed been used."
McCain, speaking to Fox News, said in his view the red line "was crossed."
Feinstein, an important voice on matters of intelligence and security, also said it is "clear" those lines have been crossed and "action must be taken to prevent larger scale use."
She added, in a statement: "Syria has the ability to kill tens of thousands with its chemical weapons. The world must come together to prevent this by unified action which results in the secure containment of Syria's significant stockpile of chemical weapons. On the basis of this new assessment, which is matched by France and the United Kingdom, I urge the United Nations Security Council -- including Russia -- to finally take strong and meaningful action to end this crisis in Syria."
Obama has said the use of chemical weapons would be a "game-changer" in the U.S. position on intervening in the two-year-old Syrian civil war. Obama said last August that "a red line for us" would be the movement or use of chemical weapons, adding "that would change my calculus."
Sen. Lindsey Graham, R-S.C., reacting to the reports Thursday, said the "number one" goal should be to "secure the chemical weapons before they fall into the wrong hands."
"I think the red line's been crossed and the question is, now what?" Graham said on Fox News.
Sen. Bob Corker, R-Tenn., also said in a statement the assessment is "deeply troubling and, if correct, means that President Obama's red line has certainly been crossed."
But Sen. Bill Nelson, D-Fla., argued that it is not in the United States' "best interest" to go into Syria. "We cannot be absolutely sure about the extent to which Assad's forces have used chemical weapons, although we know they have them," he said in a statement.
Caitlin Hayden, a spokeswoman for the White House National Security Council, said more information is needed.
"Precisely because the president takes this issue so seriously, we have an obligation to fully investigate any and all evidence of chemical weapons use within Syria," she said. "That is why we are currently pressing for a comprehensive United Nations investigation that can credibly evaluate the evidence and establish what took place. We are also working with our friends and allies, and the Syrian opposition, to procure, share and evaluate additional information associated with reports of the use of chemical weapons so that we can establish the facts."
Asked if this crossed a "red line" for the U.S., Hagel likewise said they are still trying to assess.
"It violates every convention of warfare," he said.
In a statement Thursday, a spokesperson for U.N. Secretary-General Ban Ki-moon said that he takes the letter to Congress "seriously" but that the UN is not in a position to comment on assessments based on national intelligence information.
"Senior advisers at U.N. Headquarters have been in contact with the U.S. authorities on the latest developments," the spokesperson said. "The secretary-general has already put together a technical expert team to conduct a fact-finding mission to look into all serious allegations of the possible use of chemical weapons in Syria."
According to the spokesperson, the fact-finding team is on stand-by and ready to deploy in 24 to 48 hours.
"The secretary-general has consistently urged the Syrian authorities to provide full and unfettered access to the team. He renews this urgent call today," the spokesperson said.
The Associated Press contributed to this report.