The US Congress is not authorised to green-light American military strikes against Syria as any such action would be in violation of international law, Iran's Foreign Minister Mohammad Javad Zarif said Sunday.

Iran's reaction came a day after US President Barack Obama said he was seeking congressional approval for punitive military action against the Syrian regime over its suspected use of chemical weapons against civilians, which Washington says killed more than 1,400 people.

"Mr Obama cannot interpret and construe international law for his own (benefit)," Zarif told reporters after a late afternoon cabinet meeting, the ISNA news agency reported.

"Congress cannot authorise strikes (against Syria) and that attack would be in violation of international law," he said, explaining that "only the UN Security Council -- under special conditions -- can issue authorization" for the use of force to restore international peace.

Steadfastly opposed to any military threat against Syria, Iran has condemned the use of chemical weapons there but echoed claims from Damascus that rebels fighting President Bashar al-Assad may have executed the attack.

Zarif on Sunday also repeated numerous warnings by Iranian officials and military commanders -- who have stopped short of threatening to take retaliatory action in support of Assad -- that military action against Syria would destabilise the region.

"The legality of it aside, any use of force in the region will ignite a fire which would be difficult to extinguish," he said.

Along with Russia -- another key supporter of Assad and a member of UN Security Council -- Iran has strongly backed the Syrian regime in its struggle against an uprising-turned-civil war since March 2011 that has claimed more than 100,000 lives.