Hours before President Obama arrived here to lobby world leaders to support a planned military strike against Syria, the Pentagon had to clarify Secretary of Defense Chuck Hagel's assertion that Russia provided chemical weapons to Syria and Russia President Vladimir Putin accused Secretary of State John Kerry of lying about al Qaeda's links to Syrian rebels.

Obama will seek more certain footing in the city that Peter the Great founded in 1703 and that is hosting its second global economic summit in seven years.

All five permanent members of the United Nations Security Council -- the U.S., Great Britain, France, China and Russia -- are attending the summit. Upon Putin's arrival Thursday, he and Obama shared a brief handshake and exchanged smiles during their only scheduled meeting during the summit. After Russia granted NSA leaker Edward Snowden asylum in July, Obama canceled a planned bilateral meeting with Putin that was to take place during Obama's visit to Russia.

While in St. Petersburg, Obama will seek as much support as he can find to punish the Syrian regime of Bashar Assad for what Obama asserts is an air-tight circumstantial case that he ordered a chemical weapons attack in the suburbs of Damascus on Aug. 21.

That attack, the U.S. contends, killed nearly 1,500 civilians, almost of a third of them children.

But Obama arrives with contention surrounding what top cabinet secretaries have said about the Syria conflict and Russia's role in it. Those missteps could complicate Obama's bid for broader international support. Even if they don't, they provide fodder for Russians eager to pounce on any administration fumble in an effort to shield Syria, its long-time ally, from international condemnation or a U.S.-led missile strike.

Hagel told a House hearing that Russia was a primary supplier of chemical weapons. In response to a question from Rep. Joe Wilson, R-S.C., about the origins of Syria's chemical weapons, Hagel said: "Well, the Russians supply them. Others are supplying them with those chemical weapons. They make some themselves."

The Pentagon later released a statement saying Hagel meant only to describe Russia's shipments of conventional weapons, adding modifications in Syria might make them relevant to chemical weapons use.

"Secretary Hagel was referring to the well-known conventional arms relationship between Syria and Russia," Pentagon spokesman George Little said in a statement. "The Syrian regime has a decades-old, largely indigenous chemical weapons program. Currently, Russia provides the Syrian regime a wide variety of military equipment and support, some of which can be modified or otherwise used to support the chemical weapons program."

Russian officials had no immediate reaction to Hagel's comments.

But Putin minced no words in denouncing Kerry, whom the Russian president accused of down-playing the role of al Qaeda-linked fighters within the ranks of Syria's opposition forces.

"He is lying and he knows that he is lying," Putin said. "This is sad."

At issue is Kerry's assertion that moderate elements within the Syrian opposition exert the most influence and the al Qaeda-associated group Jabhat al-Nusra is a minor player militarily and organizationally. Kerry said extremist and jihadist groups comprise less than a quarter of Syrian rebel forces.

The chairman of the Joint Chiefs of Staff, Gen. Martin Dempsey, argued in a letter last month to Rep. Eliot Engel, D-N.Y., the top Democrat on the House Foreign Affairs Committee, that figuring out which opposition group to back is a major challenge. Dempsey wrote that the faction the U.S. sides with "must be ready to promote their interests and ours" but currently they are not ready to do so.

Assad and Putin counter that the regime is under attack from terrorists and is justified in battling them. Putin has also said it is "ludicrous" to accuse the Syrian army of using chemical weapons when they hold, overall, most of the military advantage. Kerry and other U.S. officials have said Syrian armed forces were frustrated at their inability to eject rebels from the suburbs east of Damascus and unleashed chemical weapons to gain the upper hand.

In Stockholm on Wednesday, Obama admitted relations with Russia have "hit a wall" and while the two leaders are likely to have fleeting exchanges during the economic summit, no formal talks will occur and Syria will continue to complicate relations. Russia has vowed to oppose any efforts within the Security Council to authorize military strikes against Syria.

Obama met Thursday with Japanese Prime Minister Shinzo Abe, where they discussed a variety of issues including Syria. Before their meeting, the president repeated his call for military action, telling reporters "that the use of chemical weapons in Syria is not only a tragedy but also a violation of international law that must be addressed."

On Friday, Obama will huddle with French President Francois Hollande and Chinese President Xi Jinping. Syria will figure prominently in Obama's discussions with the Japanese and French leaders but play almost no role in talks with China's president due to China's preference to sit out the global debate over Syria.

Obama won narrow approval in the Senate Foreign Relations Committee on Wednesday of the authorization to use force against Syria. Senators re-wrote the authorization to specifically forbid U.S. combat troops in the Syria civil war and place an initial 60-day time limit on the attack.

Obama expressed confidence Congress would ultimately approve the authorization but said in Stockholm he's nervous the world may be afraid to hold Syria accountable for chemical weapons use.

"You can always find a reason not to act," Obama said. "But we can send a very strong message. We can change Assad's calculus about using them again. We can degrade his capabilities to use it again."

Obama will repeat that plea in numerous encounters with world leaders here. Issues arising over Hagel and Kerry's push for military action against Syria have garbled Obama's message slightly but White House advisers hope to emerge from the summit with more coalition partners -- at least rhetorically -- and a process that leaves Putin out-numbered, if not marginalized.