US Republican Senator John McCain has said he does not back the Senate panel draft resolution authorising use of force in Syria.
"There are a number of people who are unhappy," McCain told reporters on Capitol Hill.
The Senate Foreign Relations Committee draft was narrower than the request made by President Obama, and the panel, of which McCain is a member, may vote on it later today.
Senator McCain has been calling for US intervention in the civil war for many months now.
Obama made a personal appeal to the international community to unite in military action against 'barbarism' in Syria.
President Obama has received the support of prominent Republicans as he tries to gain backing for military action in Syria.
President Obama and his team are engaged in frenzied lobbying as lawmakers prepare to vote on a possible military strike in Syria.