ST. PETERSBURG, Russia — President Barack Obama said Wednesday that he didn’t set the “red line” against Syria for the use of chemical weapons.

Speaking at a press conference in Stockholm ahead of an economic summit in Russia, where he will seek support for a U.S. military strike against Syria, Obama said the “red line” he talked about a year ago against Syria’s use of chemical weapons wasn’t his but an international standard.

“I didn’t set a red line, the world set a red line ,” Obama said. “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 because we give lip service to the notion that these international norms are important.”

At an August 2012 White House press conference, Obama warned that “we have been very clear to the Assad regime, but also to other players on the ground, that 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 Syrian government for a chemical attack that did cross the so-called red line. A major argument for granting the authorization is that Obama and the United States would look weak if they did not act.

Obama said Wednesday that he didn’t pluck the idea of a red line “out of thin air,” but was referring to a global treaty banning the use of chemical weapons, “which the overwhelming consensus of humanity says is wrong.”

Yet the difficulty Obama faces in achieving a global consensus was illustrated at the press conference with Swedish Prime Minister Fredrik Reinfeldt, who decried the use of chemical weapons and said he understood Obama’s predicament but said Sweden wants United Nations involvement and a political resolution to the carnage in Syria.

“I understand the problem of not having a reaction to abuse of chemical weapons and what kind of signal that sends to the world,” Reinfeldt said. “But this small country will always say, ‘Let’s put our hope into the United Nations, let us push on some more to get a better situation.’”

Obama, who was asked how he could square his Nobel Peace Prize with a military attack, staunchly defended his push for a strike, evoking the exposure of children to chemical weapons. The Nobel Foundation is based in Stockholm.

“The moral thing to do is not to stand by and do nothing,” Obama said. He later added, “I do have to ask people if in fact you’re outraged by the slaughter of innocent people, what are you doing about it?”

Obama said he expects Congress to give him the authorization he seeks to launch a military strike. But he left the door open to acting unilaterally: “As commander in chief, I always preserve the right and the responsibility to act on behalf of America’s national security.”

He added that he doesn’t believe he was required to ask Congress, but said, “I did not take this to Congress just because it’s an empty exercise. I think it’s important to have Congress’ support on it.”

Though Obama has chosen to act before a U.N. investigation is completed, he said U.S. intelligence shows there’s no doubt that chemical weapons were used by the regime.

“Keep in mind I’m somebody who opposed the war in Iraq and am not interested in repeating mistakes of us basing decisions on faulty intelligence,” Obama said.

The press conference came hours after Russian President Vladimir Putin warned the U.S. against military strikes in Syria, saying that without the sanction of the United Nations any assault would be “inadmissible and can only be interpreted as an aggression.”

Putin said in an interview with the Associated Press that the Russian government has provided some components of the S-300 air-defense missile system to Syria but has suspended shipments “for now.” He suggested that Russia may sell the potent missile systems elsewhere if Western nations attack Syria without U.N. Security Council backing.

Russia has routinely vetoed sanctions against Syria in the United Nations, but Putin didn’t rule out supporting a U.N. resolution to support military strikes if it’s proven that the Syrian regime used chemical weapons.

He made clear his threshold for such support is high, calling it “absolutely absurd” that the government would use chemical weapons at a time when it was closing in on the rebels.

Though he canceled a pre-summit meeting with Putin, Obama said he remains hopeful he can convince Putin to drop his support for the Syrian regime. He said the U.S. shares some concern with Russia “about certain elements of the opposition,” but that “it is not possible for Mr. Assad to regain legitimacy in a country where he’s killed tens of thousands of his own people. That will not happen.”

But, he said of Putin, “I will continue to engage him because I think that international action would be much more effective.”

U.S.-Russia relations have been deteriorating for 18 months, including divisions over Russia’s recently enacted anti-gay laws. Obama made it plain he will bring up the issue, lauding his Swedish hosts without prompting for treating gays and lesbians “equally under the law.” Obama, who will meet Thursday with human rights activists in St. Petersburg, said the U.S. and Sweden “stand up for universal human rights not only in America and Europe but beyond, because we believe that when these rights are respected, nations are more successful and our world is safer and more just.”

In his interview, Putin insisted he and Obama could have constructive talks – even though Putin said he was disappointed Obama canceled the meeting with him in Moscow.

A White House official said that although there was no plan for a formal meeting with Putin at the summit in St. Petersburg, the White House “would expect the two presidents to have an opportunity to speak on the margins of the various meetings of the G-20.”

Obama will hold formal bilateral meetings with Chinese President Xi Jinping, Japanese Prime Minister Shinzo Abe and French President Francois Hollande.

Putin downplayed his frosty relationship Obama, which Russia analysts have said is among the worst in U.S.-Russian and U.S.-Soviet leader relationships.

“President Obama hasn’t been elected by the American people in order to be pleasant to Russia,” Putin told the AP. “And your humble servant hasn’t been elected by the people of Russia to be pleasant to someone, either.”

“We work, we argue about some issues. We are human,” Putin said. “Sometimes one of us gets vexed. But I would like to repeat once again that global mutual interests form a good basis for finding a joint solution to our problems.”

In a sign that the U.S. surveillance program continues to be a source of concern even among U.S. allies, the first question Obama got from a Swedish reporter at the press conference was about the intrusive National Security Agency program.

Obama insisted the U.S. is not “snooping at people’s emails and or listening to their phone calls.”

The program’s focus, he said, is on counterterrorism and cyber security.

White House briefing with Obama and 'red line' at 34:16