The Syrian opposition bloc says "elements in the U.S. Congress" have been delaying the Obama administration's efforts to step up support for rebel forces.

President Barack Obama recently said the U.S. is willing to send weapons to the opposition. Even so, Washington has been reluctant to arm the rebels battling the army of President Bashar Assad because radical Islamic groups, including some with al-Qaida links, have emerged as their most effective fighting force.

The Western-backed Syrian National Coalition urged Congress to back arms deliveries to the rebels as Assad's regime intensifies attacks. It says it's "deeply concerned by reports indicating that elements of the U.S. Congress" are delaying weapons.

The coalition will ensure "that arms will not reach extremist elements," it said in a statement late Thursday.