By Matt Spetalnick
WASHINGTON (Reuters) - The United States has concluded that Syrian President Bashar al-Assad's forces used chemical weapons against rebel fighters in Syria and President Barack Obama has decided to supply direct military assistance to the Syrian opposition, the White House said on Thursday.
The new intelligence assessment, which followed Obama's demand for conclusive proof that chemical weapons had been deployed, could put pressure on Washington to respond aggressively to the crossing of what Obama himself had called a "red line."
With outgunned rebel forces desperate for weapons after suffering a series of setbacks on the battlefield, Ben Rhodes, Obama's deputy national security adviser, said the president had decided to provide "direct military support" to the opposition.
But Rhodes would not specify whether that will include lethal aid, such as weapons, which would mark a reversal of Obama's resistance to arming the rebels. He said only that the military assistance would be different in "both scope and scale" to what had been authorized before, which included non-lethal equipment such as night-vision goggles and body armor.
The announcement followed intensive deliberations between Obama and his national security aides on Syria amid mounting pressure at home and abroad for him to act more forcefully in the conflict, including a sharp critique of his policy from former President Bill Clinton.
After months of investigation, the White House finally laid out its conclusions on chemical weapons use by Assad's forces, but stopped short of threatening specific actions in response to what Obama said would be a "game changer" for Washington's handling of the conflict.
"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 told reporters.
"Our intelligence community has high confidence in that assessment given multiple, independent streams of information," he said. "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."
Pressed on what the United States would do next, Rhodes said the White House would share the information with Congress and U.S. allies but will "make decisions on our own time line."
Obama's earlier warnings had been widely interpreted to leave open the prospects of U.S. military action, though Obama has made clear he will not put American "boots on the ground" in Syria.
Clinton's call for deeper U.S. engagement in Syria's civil war put the Obama administration on the defensive just a day before Western envoys are expected to hear rebel pleas for weapons in the face of setbacks to Assad's forces and his Lebanese Hezbollah allies.
"Some people say, ‘OK, see what a big mess this is? Stay out!' I think that's a big mistake," the former Democratic president, who until now had avoided criticizing Obama's foreign policy, was quoted as saying in New York this week.
While Obama has resisted U.S. military entanglement in Syria during more than two years of conflict there, the rebels' deteriorating situation on the ground has prompted a reassessment of Washington's options, including the possibility of reversing policy and sending arms to the opposition.
Following a series of meetings on Syria this week among Obama's top aides, Rhodes said: "The president has made a decision about providing more support to the opposition, that will involve providing direct support to the (Supreme Military Council), that includes military support."
The arrival of thousands of seasoned Iran-backed Hezbollah Shi'ite fighters to help Assad combat the mainly Sunni rebellion has shifted momentum in the civil war, which the United Nations said on Thursday has killed at least 93,000 people.
Syria will be high on the agenda at the Group of Eight summit in Northern Ireland next week, and Obama plans to consult with them on the way forward. He can also can expect a difficult encounter with President Vladimir Putin of Russia, which has backed Assad.
(Additional reporting by Susan Heavey, Jeff Mason, Susan Cornwell, Mark Felsenthal, Roberta Rampton; Editing by Jim Loney)