T he Syrian crisis is not on the official agenda for the two-day Group of 20 global economic summit in Saint Petersburg, but leaders are expected to discuss it on the sidelines.

Russia, Syria’s main supplier of arms, and China have already vetoed three U.N. Security Council resolutions on Syria.

Speaking ahead of the summit, Chinese Vice Foreign Minister Zhu Guangyao said Thursday any military action against Syria would cause a hike in oil prices and have a “negative impact” on the global economy.

On Wednesday, Russian President Vladimir Putin warned Western strikes without U.N. Security Council approval would be an unacceptable “aggression.” But he said he would support a strike if there were “convincing” proof that Damascus used chemical weapons.

“Only the U.N. Security Council could sanction the use of force against a sovereign state,” Mr. Putin told the Associated Press and Russia’s state Channel 1 television network. “Any other pretext or method which might be used to justify the use of force against an independent sovereign state is inadmissible and can only be interpreted as an aggression.”

Mr. Putin urged the U.S. to present “convincing” evidence about chemical weapons to the United Nations.

He said Russia has suspended the delivery of S-300 surface-to-air missile components to Syria, but would reconsider if steps are taken that “violate international norms.”

UN hopes for political solution to the situation in Syria Even as the U.S. pushes for possible strikes, U.N. officials continue to look for a political settlement to the conflict. Officials say U.N.-Arab League envoy on Syria Lakhdar Brahimi is headed to St. Petersburg to help U.N. chief Ban Ki-moon organize a Syrian peace conference. U.N. Secretary-General Ban Ki-Moon has said any use of chemical weapons in Syria is an “outrageous war crime,” and he called on the Security Council to “unite and develop an appropriate response” to bring the perpetrators to justice. However, he said a political solution to the crisis in accordance with the U.N. Charter is the best way to proceed.