Khalil Ashawi / REUTERS A boy carries a weapon as he walks with members of the Free Syrian Army on a damaged street filled with debris in Deir ez-Zor on June 12, 2013

American officials confirmed Thursday that the Syrian government has used chemical weapons against rebel groups in the country’s two-year civil war, setting the stage for U.S. military assistance to opposition fighters and potential intervention.

The development, announced Thursday by Deputy National Security Adviser Ben Rhodes, puts the government of Syrian President Bashar Assad over President Barack Obama’s “red line” announced in August 2012 promising severe consequences for the use of chemical weapons.

“We have been very clear to the Assad regime, but also to other players on the ground, that a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized,” Obama said at the time. “That would change my calculus. That would change my equation.”

On April 25, 2013, the White House informed members of Congress that the government believed that Syrian forces had used the nerve agent sarin on a “small scale,” according to physiological evidence collected. Obama and aides have stressed the need for a full investigation into the use — an investigation that has now resulted in confirmation of the use of chemical weapons.

“Following a deliberative review, our intelligence community assesses that the Assad regime has used chemical weapons, including the nerve agent sarin, on a small scale against the opposition multiple times in the last year,” Rhodes said in a statement Thursday. “Our intelligence community has high confidence in that assessment given multiple, independent streams of information.”

“The intelligence community estimates that 100 to 150 people have died from detected chemical weapons attacks in Syria to date; however, casualty data is likely incomplete,” he added.

On a conference call with reporters, Rhodes said the U.S. will be increasing its direct support to the Supreme Military Council, but did not specify whether lethal aid will flow into Syria. “It is both the political and military opposition that are and will be receiving assistance,” he said.

“The President has made a decision on providing more support to Syrian opposition,” Rhodes said, declining to “layout an inventory” of that assistance or say if lethal aid will be provided. “That includes military support.”

Rhodes said no decision had been made to pursue a no-fly zone, adding there’s no “clear guarantee” it would help.

“The United States and the international community have a number of other legal, financial, diplomatic, and military responses available,” he said. “We are prepared for all contingencies, and we will make decisions on our own timeline.”

In a joint statement, Senators Lindsey Graham and John McCain encouraged Obama to provide lethal assistance to the rebels.

“The President’s red line has been crossed,” they said. “U.S. credibility is on the line. Now is not the time to merely take the next incremental step. Now is the time for more decisive actions.”

Brendan Buck, a spokesman for Speaker of the House John Boehner, said, “It is long past time to bring the Assad regime’s bloodshed in Syria to an end. As President Obama examines his options, it is our hope he will properly consult with Congress before taking any action.”

Rhodes said the White House is updating members of Congress on the developments and that the U.S. has briefed allies and the U.N. on its investigation and has informed Russia, one of the Syrian government’s few supporters.