US President Barack Obama has said he is confident that Congress will vote in favour of military action in Syria and said the United States had a broader plan to help rebels defeat President Bashar al-Assad's forces.

During a meeting with congressional leaders at the White House on Tuesday, Obama called for a prompt vote by the Congress and reiterated that any US action would be limited in scope and not a repeat of Iraq or Afghanistan. 

"What we are envisioning is something limited. It is something proportional. It will degrade Assad's capabilities," Obama said.

"At the same time we have a broader strategy that will allow us to upgrade the capabilities of the opposition," he said. 

Obama said he was willing to address concerns among politicians about the motion to authorise the use of force that the White House sent to Congress. "I am confident that those concerns can be addressed," he added.

"I would not be going to Congress if I wasn't serious about consultations and believing that by shaping the authorisation to make sure we accomplish the mission, we will be more effective." 

Republican Speaker of the House of Representatives John Boehner, Democratic House leader Nancy Pelosi, and Republican Senate leader Mitch McConnell were present at the meeting along with the chairs of congressional committees that deal with national security and the armed services.

Asked whether he was confident Congress would vote in favour of a strike, Obama said: "I am." 

Obama reiterated his "high confidence" that the Syrian government used chemical weapons against its people on August 21 in a Damascus suburb.

The president said that posed a serious national security threat to the United States and to the region. 

Source: Agencies