no military solution to the Syrian conflict." .
Putin, Assad's most important ally, was isolated on Syria at a Group of Eight meeting in June, the last big meeting of world powers. He could now turn the tables on Obama, who recently likened him to a "bored kid in the back of the classroom."
Only France, which is preparing to join U.S. military action, rallied behind Obama.
"We are convinced that if there is no punishment for Mr. Assad, there will be no negotiation," French Foreign Minister Laurent Fabius said before leaving for St. Petersburg.
With backing by Beijing and Moscow unlikely at the U.N. Security Council, where both have veto powers, Obama is seeking the approval of the U.S. Congress.
Putin says rebel forces may have carried out the poison gas attack and that any military strike without Security Council approval would violate international law, a view which is now increasingly openly being supported by others.
He has no one-on-one talks scheduled with Obama but hopes to discuss Syria at a dinner with all the leaders. United Nations Secretary General Ban Ki-moon and U.N. special envoy Lakhdar Brahimi were also in St. Petersburg, hoping to secure agreement on holding an international peace conference on Syria.
Putin's press secretary, Dmitry Peskov, portrayed the "camp of supporters of a strike on Syria" as divided and said: "It is impossible to say that very many states support the idea of a military operation."
One national leader attending the summit said there appeared to be little chance of a rapprochement between Putin and Obama, whose relations have soured following Russia's offer of asylum to former U.S. spy agency contractor Edward Snowden.
Foreign ministers from the key states in the G20 - which includes all five permanent U.N. Security Council members - will also discuss Syria on the sidelines of the meeting.
Any G20 decision on Syria would not be binding but Putin would like to see a consensus to avert military action in what would be a significant - but unlikely - personal triumph.
LOSS OF HARMONY
The G20 achieved unprecedented cooperation between developed and emerging nations to stave off economic collapse during the