"I didn't set a red line. The world set a red line," he said in Stockholm on Wednesday, asserting that the red line he outlined last year regarding Syria's use of chemical weapons came from international treaties and past congressional action.

Obama, who is on his way to St. Petersburg, Russia, to attend a G-20 Summit, said the global red line came when governments representing 98 percent of the world's population "passed a treaty forbidding (chemical weapons) use, even when countries are engaged in war."

"My credibility is not on the line -- the international community's credibility is on the line," he said at a joint news conference with Swedish Prime Minister Fredrik Reinfeldt, who opposes military intervention without UN approval.

UN Secretary-General Ban Ki-moon too has warned that any military strike against Syria without the world body's sanction would be illegal. The use of force is lawful only when in exercise of self-defence in accordance with Article 51 of the United Nations Charter and/or when the Security Council approves such action, he told reporters on Tuesday before leaving for St. Petersburg.

Calling on Security Council members to unite and develop an appropriate response should allegations regarding the use of chemical weapons prove true, Ban also asked them to "consider the impact of any punitive measure on efforts to prevent further bloodshed and facilitate a political resolution of the conflict".

Asking the global community to act on Wednesday, Obama said: "I respect the UN process but are we going to try to find a reason not to act? And if that's the case, then I think the (world) community should admit it?"

"We agree that the international community cannot be silent," Obama said, adding that a team of UN investigators has done "heroic work".

However, the UN team's mandate was only to determine if chemical weapons had been used, Obama said, repeating that US intelligence has confirmed that beyond any reasonable doubt, and has further confirmed that President Bashar al-Assad's regime "was the source".

Obama spoke as the Senate Foreign Relations Committee prepared to consider a resolution that would give the President authority to carry out a strike against Syria, for a period of 60 days, with one 30-day extension. It also makes clear there would be no US boots on the ground.

Democratic and Republican lawmakers had on Tuesday agreed on the wording of a revised resolution after posing tough questions to Secretary of State John Kerry, Defence Secretary Chuck Hagel and General Martin Dempsey, the chairman of the Joint Chiefs of Staff. But the new resolution ran into opposition from the 2008 Republican presidential candidate John McCain, an outspoken advocate of action against Syria who wants more than cruise missile strikes and other limited action.

Asked if he supported the resolution crafted by Democratic panel chairman Bob Menendez and Republican Bob Corker, McCain said, "In its current form, I do not." Earlier this week, he had threatened to vote against the original White House draft resolution unless Obama promised greater support to Syria's rebels. McCain then expressed support after meeting Obama at the White House.


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