WASHINGTON -- U.S. intelligence has concluded with "varying degrees of confidence," that the Syrian government has twice used chemical weapons in its fierce civil war, the White House and other top administration officials said Thursday.
However, officials also said more definitive proof was needed and the U.S. was not ready to escalate its involvement in Syria beyond non-lethal aid, despite President Barack Obama's repeated public assertions that Syria's use of chemical weapons, or the transfer of its stockpiles to a terrorist group, would cross a "red line."
The White House disclosed the new intelligence Thursday in letters to two senators, and Defense Secretary Chuck Hagel, traveling in Abu Dhabi, also discussed it with reporters. The letters were sent in response to questions from members of Congress who are eager for the administration to arm the rebels or get involved militarily.
The Syrian civil war has dragged on for more than two years, with an estimated 70,000 dead. In addition to members of Congress, Leon Panetta and Hillary Rodham Clinton, as secretaries of defense and state, have urged Obama to increase U.S. involvement.
"Our intelligence community does assess, with varying degrees of confidence, that the Syrian regime has used chemical weapons on a small scale in Syria, specifically, the chemical agent sarin," the White House said in its letters, which were signed by Obama's legislative director, Miguel Rodriguez.
Shortly after the letters were made public, Secretary of State John Kerry said on Capitol Hill that there were two instances of chemical weapons use.
It was not immediately clear what quantity of weapons might have been used, or when or what casualties might have resulted. Hagel said many of those details were classified.
Sarin is an odorless nerve agent that can be used as a gas or a liquid, poisoning people when they breathe it, absorb it through their skin or eyes, or take it in through food or water. In large doses, sarin can cause convulsions, paralysis and death. According to the Centers for Disease Control and Prevention, people usually recover from small doses, which may cause confusion, drooling, excessive sweating, nausea and vomiting.
The Aum Shinrikyo cult used sarin in attacks in the Tokyo subway system in 1995 that killed 12 people and sickened thousands.
Obama has said the use of chemical weapons would be a "game-changer" in the U.S. position on intervening in the Syrian civil war, and the letter to Congress reiterated that the use or transfer of such weapons in Syria was a "red line for the United States." However, officials quickly made clear that a stepped up U.S. response was not imminent.
A senior defense official said the White House letter was not an "automatic trigger" for policy decisions on the use of military force. The official alluded to past instances of policy decisions that were based on what turned out to be flawed intelligence, such as the Bush administration's decision to invade Iraq after concluding that Saddam Hussein had weapons of mass destruction, including nuclear weapons.
Lawmakers from both parties sounded less than patient in this case.