Syria has crossed a "red line" with its use of chemical weapons, including the nerve agent sarin gas, against rebels, a move that is prompting the United States to increase the "scale and scope" of its support for the opposition, the White House said Thursday.
The acknowledgment is the first time President Barack Obama's administration has definitively said what it has long suspected -- that President Bashar al-Assad's forces have used chemical weapons in the ongoing civil war.
"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," Ben Rhodes, the deputy national security adviser for strategic communications, said in a statement released by the White House.
"While the lethality of these attacks make up only a small portion of the catastrophic loss of life in Syria, which now stands at more than 90,000 deaths, the use of chemical weapons violates international norms and crosses clear red lines that have existed within the international community for decades," Rhodes added.
The administration also appeared to indicate that it was stepping up its support of the rebels, who have been calling for the United States and others to provide arms needed to battle al-Assad's forces.
"Put simply, the Assad regime should know that its actions have led us to increase the scope and scale of assistance that we provide to the opposition, including direct support to the (rebel Supreme Military Council). These efforts will increase going forward," Rhodes' statement said.
'Our own timeline'
Rhodes later told reporters on a conference call that the president has made a decision about military support for the rebels but stopped short of saying the U.S. government would put weapons in the hands of rebels.
The president has previously said he did not foresee a scenario with "American boots on the ground in Syria."
Rhodes also said no decision has been made by Obama over whether to institute a no-fly zone in Syria, something rebel forces have said is needed to halt al-Assad's aerial bombardment of their strongholds.
The administration plans to share its findings with Congress and its allies, and it will make a decision about how to proceed "on our own timeline," Rhodes said.
Syria will be among the chief topics for Obama at the Group of Eight summit in Northern Ireland next week, where Rhodes said the president will share the U.S. findings on al-Assad's use of chemical weapons.
"We'll be consulting at the G8 and the United Nations about what might be necessary," Rhodes said.
Syria has long maintained that rebels, not government forces, are behind the use of chemical weapons. It also went to the United Nations with its claims, but al-Assad would not allow U.N. inspectors into the country to try to verify the claims.
The administration believes that al-Assad's government maintains control of the chemical weapons and that there is "no reliable, corroborated reporting to indicate that the opposition in Syria has acquired or used chemical weapons," Rhodes statement said.
Rhodes gave no indication of how many times al-Assad's forces used chemical weapons, but a U.S. Senate source briefed on the matter said the administration believes Syria used such weapons on at least eight occasions.
No 'half measures'
The White House announcement comes at a critical time for the Syrian opposition, which has suffered a series of significant losses in recent weeks.
The setbacks in large part have coincided with the arrival of thousands of Hezbollah Shiite fighters, backed by Lebanon and Iran, to reinforce al-Assad's forces battling the mainly Sunni uprising.
After months of gaining ground, the rebels this month lost Qusayr -- one of its strongholds near the Lebanese border -- that was considered essential for its supply route.
U.S. Sen. John McCain, who has repeatedly called on the administration to step up its support of the rebels, said on CNN's Situation Room that the rebels need anti-tank and anti-aircraft weapons.
"They need a lot more military assistance," McCain, an Arizona Republican, said, adding that the United States and its allies also need to "establish a 'no-fly' zone to create a safe area" within Syria.
"You can't do it with half measures. You can't do it with just supplying weapons," he said.
McCain said the options were not ideal and a response will not be easy. But doing nothing, he said, would be catastrophic.
Until now, the United States has limited its aid to rebels, providing communications equipment, medical supplies and food.