US President Barack Obama has asked Congress to approve $500m (£294m) to train and equip members of the "moderate Syrian armed opposition".
The funds would help Syrians "defend themselves against regime attacks", the White House said in a statement.
It would also be aimed at countering extremists such as the Islamic State in Iraq and the Levant (Isis), it added.
The advance of Isis in neighbouring Iraq has led to pressure on Mr Obama from some lawmakers.
Last month Mr Obama hinted at increased help for the Syrian opposition in a speech at the military academy at West Point.
He said he would work with Congress to "ramp up support for those in the Syrian opposition who offer the best alternative to terrorists and a brutal dictator."
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Syria crisis: Obama asks Congress for $500m for rebels