White House officials on Thursday said President Obama has decided to provide "military support" to Syria's anti-government rebels after acknowledging for the first time that Syrian President Bashar al-Assad had used chemical weapons against opposition forces, crossing a "red line" that the president said would lead to deeper U.S. intervention in the conflict.

The White House on Thursday refused to outline the specific actions that Obama would take, neither committing to establishing a no-fly zone over the country nor providing arms to the rebel forces as his critics have urged. However, administration officials later told The Washington Examiner the U.S. would send light arms and ammunition to the Syrian rebels in coming weeks.

"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," said Ben Rhodes, deputy national security adviser for strategic communications and speechwriting, adding that the administration would outline further action on its own timeline. "The president has been clear that the use of chemical weapons -- or the transfer of chemical weapons to terrorist groups -- is a red line for the United States."

Obama has faced growing pressure to provide direct military aid to the Syrian opposition as the death toll there has risen beyond 90,000 people and Assad's regime has put the rebels on the defensive.

"Providing arms alone [in Syria] is not sufficient," said Sen. John McCain, R-Ariz. "The president must rally an international coalition to take military actions."

McCain announced from the Senate floor that Obama had decided to supply the rebels with lethal weaponry. He then backtracked and said only that the president had finally acknowledged the use of chemical weapons against the Syrian opposition.

U.S. allies, such as Israel, weeks ago condemned Assad for deploying chemical weapons, but Obama refrained from saying his red line had been crossed.

Senior White House officials have been split on how to respond to the widespread violence. Obama previously shot down an administration plan to arm the rebels, concerned that such weapons would fall into the hands of extremist groups. He now appears to be on the verge of changing that calculus.

For their part, congressional Republicans insisted that Obama consult them before making any major commitments in Syria.

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

Rhodes said intelligence officials estimate that 100 to 150 people in Syria have been killed by chemical weapons, just a small percentage of the total death count but enough to prompt a more aggressive White House response. Administration officials this week held a series of meetings to coordinate a strategy for dealing with Syria before Obama heads to the G-8 summit in Northern Ireland in coming days.

But such caution drew criticism this week, even from Obama's Democratic predecessor, President Clinton.

"Some people say, 'OK, see what a big mess this is? Stay out!' " Clinton said at a private event in New York City, telling McCain, "I think that's a big mistake. I agree with you about this."