'I didn't set a red line; the world set a red line,' Obama says President Barack Obama meets with congressional leaders to discuss the Syria in the cabinet room of the White House on September 3, 2013. Shown are (L-R): Senate Assistant Majority Leader Dick Durbin, National Security Adviser Susan Rice, House Speaker John Boehner, Obama, and House Minority Leader Nancy Pelosi. UPI/Dennis Brack/Pool 5 (UPI) -- Striking Syria over nerve gas is a world issue, not his own, President Obama said before going to Russia Thursday for a summit led by President Vladimir Putin. "I didn't set a red line," Obama said in a news conference in Stockholm. The world set a red line. "The world set a red line when governments representing 98 percent of the world's population said the use of chemical weapons are abhorrent and passed a treaty forbidding their use even when countries are engaged in war," he said. "Congress set a red line when it ratified that treaty," he added. And so, when I said in a press conference that my calculus about what's happening in Syria would be altered by the use of the chemical weapons, which the overwhelming consensus of humanity says is wrong, that wasn't something I just kind of made up. Obama said in an Aug. 20, 2012, news conference: "A red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized. That would change my calculus. That would change my equation. Obama is seeking approval from Congress to launch airstrikes against the Assad regime. A sharply divided Senate Foreign Relations Committee voted 10-7 Wednesday to give Obama limited authority to use force against Syria. The full Senate is expected to vote on the measure next week after Congress returns from recess. The House is likely to hold off its vote until the following week after a long debate, administration officials told The New York Times. A major congressional argument for authorizing the attack suggests Obama and the United States would look weak if they did not act. At the news conference Wednesday, Obama added: "My credibility is not on the line. The international community's credibility is on the line. And America and Congress' credibility is on the line. Obama again blamed Syrian President Bashar Assad for an Aug. 21 attack the U.S. administration alleges was a sarin gas attack that killed more than 1,400 people in rebel-held suburbs of Damascus, the Syrian capital. The administration has not shown evidence Assad ordered the alleged sarin use, but Obama said he was responsible. "We believe very strongly, with high confidence, that in fact chemical weapons were used and that Mr. Assad was the source," Obama said. Syria denies using chemical weapons and alleges opposition rebels are responsible. Obama was to arrive in St. Petersburg around 2 p.m. EDT) Thursday for the annual summit of the Group of 20 major industrialized and developing nations. The leaders meeting normally focuses on the world's economy, but Syria is widely expected to overshadow the meeting. Obama was originally scheduled to meet with Putin ahead of the summit but canceled the visit because of U.S.-Russia differences over Syria and Russia's refusal to hand over National Security Agency leaker Edward Snowden. Obama went to Sweden instead. Putin has opposed any retaliatory attack on Syria, calling such action a violation of international law. In St. Petersburg, Obama is to meet with French President Francois Hollande, who supports a strike on Syria, and Chinese President Xi Jinping, who opposes such action. Obama's first scheduled meeting Thursday is with Japanese Prime Minister Shinzo Abe, who has distanced himself from the Syria dispute. Obama has no scheduled meetings with Putin in St. Petersburg. The New York Times said such a meeting would be typical with a summit host. Obama is to return to Washington late Friday.