White House officials on Thursday said that Syrian President Bashar al-Assad's regime used chemical weapons repeatedly against anti-government rebels, acknowledging the leader had crossed the "red line" that President Obama said would warrant deeper U.S. intervention in the nation's civil war.

Obama has agreed to provide "military support" to Syrian rebels, Deputy National Security Advisor for Strategic Communications Ben Rhodes said, but he refused to specify the actions.

"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.

He added, "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, as there has long been an established norm within the international community against the use of chemical weapons."

The White House has not yet committed to providing lethal weaponry to the anti-government rebels or establishing a no-fly zone over Syria.

"We are going to make decisions about further action on our own timeline," Rhodes told reporters.