President Barack Obama has asked Congress for $500m (£294m) to strengthen more moderate Syrian rebels.
He made the request with the conflicts in Syria and Iraq becoming increasingly intertwined against the same Sunni extremist group.
Mr Obama’s bid for the money for training and arms to the opposition in effect opens a second front in the fight against militants spilling over Syria’s border and threatening to overwhelm neighbouring Iraq.
The train-and-equip mission would be overseen by the Pentagon and would mark a significant expansion of previous covert effort to arm the more moderate rebels who are fighting both the extremists and forces loyal to Syrian President Bashar Assad.
The president has long been reluctant to arm the opposition, in part because of concerns that weapons may fall into extremist hands.