he believes the Assad regime used poison gas against its own people last month.

The US President's been speaking in Stockholm after talks with the Swedish Prime Minister, Fredrik Reinfeldt.

He said US intelligence leaves little room for doubt.

 Russian President Vladimir Putin still maintains his view that he has not ruled out military strikes against Syria but warned the use of force without UN approval would be an "aggression" and a violation of international law.

Meanwhile, Mr Obama, who believes he will get Congressional backing for strikes, said the international community could not "be silent" in the face of "barbarism".

He warned that failure to respond to last month's chemical attack - which the US holds the Syrian government responsible for - would "only increase other attacks", and that he would continue to seek international support for holding the regime accountable.

Mr Obama was addressing the situation in Syria at a news conference in Sweden.

As he spoke, Syria's deputy foreign minister said the regime would not give in to threats of a US-led military strike against the country, even if it meant the start of a third world war.

Putin's Standpoint

Earlier, in an interview in Moscow ahead of tomorrow's G20 summit in St Petersburg, Mr Putin said he could back a UN resolution.

He said if convincing evidence emerged that Syrian President Bashar al Assad had used poison gas on his own people then Russia would be "ready to act in the most decisive and serious way".

Russian missile cruiser Moskva is reportedly heading to the Mediterranean

US military action moved a step closer as President Obama won support from leading opposition Republicans and US Secretary of State John Kerry urged senators not to succumb to "armchair isolationism".

Mr Kerry told the Senate Foreign Relations Committee, which finalised the draft resolution, that the US must "stand up and act" in the face of "undeniable" evidence that Mr Assad gassed his own people.

The US says it has proof that the Assad regime was behind sarin gas attacks that it believes killed at least 1,429 people on the outskirts of Damascus on August 21.

President Obama has said that any strikes could pave the way for regime change in Syria.