But while regional governments have been funding weapons supplies for the rebels, the United States and its closest allies, including Britain and France, have been reluctant to do so.
This week, demands from numerous American lawmakers that Obama authorize the delivery of arms — despite persistent U.S. public reluctance reflected in opinion polls — escalated after the rebels’ loss of a key town near the Lebanese border and reports that government forces were massing with Hezbollah and Iranian fighters to retake rebel-held portions of the northern city of Aleppo.
Officials described Obama’s decision as a gradual one, as intelligence assessments about chemical weapons use became more firm. After an initial, inconclusive assessment in April, the president “directed our intelligence community to further investigate the use of chemical weapons and to seek credible and corroborative information,” Rhodes said in a briefing for reporters Thursday afternoon.
The U.S. investigation, he said, was conducted separately from, but in conjunction with, a U.N. effort to confirm chemical weapons use in Syria.
“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. “Our intelligence community has high confidence in that assessment given multiple, independent streams of information.”
Intelligence committees in Congress were briefed on the arms decision earlier this week and on the chemical weapons conclusions on Thursday.
Republican Sens. John McCain (Ariz.) and Lindsey O. Graham (S.C.) welcomed the chemical weapons assessment. The two have been among the sharpest critics of the administration, saying it has not been doing enough to help the rebels.
“U.S. credibility is on the line,” they said in a joint statement. “Now is not the time to merely take the next incremental step. Now is the time for more decisive actions,” they said, such as using long-range missiles to degrade Assad’s air power and missile capabilities.
Sen. Robert P. Casey Jr. (D-Pa.) said the moderate opposition forces risk defeat without heavier weapons, but he also warned that may not be enough.
“The U.S. should move swiftly to shift the balance on the ground in Syria by considering grounding the Syrian air force with stand-off weapons and protecting a safe zone in northern Syria with Patriot missiles in Turkey,” Casey said.
Such a no-fly zone would roughly parallel the NATO action in Libya two years ago. NATO has repeatedly said that it is not contemplating a similar move in Syria.
An awkward chapter
The chemical weapons assessment closes an awkward chapter for the Obama administration, in which it lagged behind two key European allies in reaching the same conclusion. France sent its dossier of chemical weapons evidence to Washington more than a week ago, and Britain had earlier provided what both countries called extremely persuasive evidence.
“A line has been crossed. Unquestionably,” French Foreign Minister Laurent Fabius said last week.
“We’ve prepared for many contingencies in Syria,” Rhodes said. “We are going to make decisions on further actions on our own timeline.”
The announcement Thursday followed days of intensive discussions among Obama’s top national security aides that administration officials said were partly a response to the rebel defeat in Qusair last week.
Idriss had spent days lobbying the White House and Congress for more help, saying that the rout in the border town undermined his military authority with Syrian civilians and opened the way for a government onslaught in Aleppo.
Greg Miller contributed to this report.