The White House confirmed to members in Congress Thursday that the Syrian government has used small amounts of chemical weapons in its fight against rebel forces, a move the White House has said crosses a "red line."
Secretary of Defense Chuck Hagel also confirmed the use of sarin, a chemical weapons agent, to reporters Thursday during his visit to Abu Dhabi.
"It violates every convention of warfare," Hagel told reporters overseas.
In the letter, sent to Sens. John McCain, R-Ariz., Bob Corker, R-Tenn., Bob Casey, D-Pa., Carl Levin, D-Mich., Lindsey Graham, R-S.C., Kelly Ayotte, R-N.H., Saxby Chambliss, R-Ga., and Bob Menendez, D-N.J., Obama confirmed what many lawmakers speculated: that with the used of chemical weapons, the Syrian regime crossed the line.
"Our intelligence community does assess with varying degrees of confidence that the Syrian regime has used chemical weapons on a small scale in Syria," the letter to lawmakers read. "We believe that the Assad regime maintains custody of these weapons and has demonstrated a willingness to escalate its horrific use of violence against the Syrian people."
The administration cautioned, however, that they are still working to confirm that Bashar Assad was fully responsible for deploying the weapons.
French, Israeli and British intelligence services have also reported they have extensive evidence that the Syrian government has increasingly been using chemical weapons.
Obama's letter to lawmakers also confirms that administration has been in communication with leaders around the world, including Assad's that the use of chemical weapons is a "red line."
The administration has asked the United Nations to launch a comprehensive investigation into how and under what circumstances the weapons were used.
How the United States and its allies react, however, remains in flux.
"The United States and the international community have a number of potential responses available, and no option is off the table."
Because of the developing reports of chemical warfare, the administration has pledged "dramatically" more humanitarian support to the region "to bring about the political transition the Syrian people deserve," the letter concludes.