Lawmakers demand 'action' in Syria after intel confirms chemical weapons use Top-ranking lawmakers on both sides of the aisle declared Thursday that the "red line" in Syria has been crossed, calling for "strong" U.S. and international intervention after administration officials revealed the intelligence community believes chemical weapons were used. Sen. John McCain, R-Ariz., and Sen. Dianne Feinstein, D-Calif., chairwoman of the Senate intelligence committee, 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." 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. President 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 in a statement. 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.