Russian president Vladimir Putin has warned the West against taking unilateral action in Syria but also said Russia "doesn't exclude" supporting a UN resolution on military strikes if a government chemical attack is proved.
On the eve of the G-20 summit in St. Petersburg, which opens on Thursday, Mr Putin said he was sorry President Barack Obama cancelled a one-on-one meeting that was supposed to have preceded it.
"President Obama hasn't been elected by the American people in order to be pleasant to Russia. And your humble servant hasn't been elected by the people of Russia to be pleasant to someone either," he said of their relationship.
"We work, we argue about some issues. We are human. 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," he said.
Mr Putin said it was "ludicrous" that the government of president Bashar Assad - a staunch ally of Russia - would use chemical weapons at a time when it was holding sway against the rebels.
"If there are data that the chemical weapons have been used, and used specifically by the regular army, this evidence should be submitted to the UN Security Council," he said. "And it ought to be convincing. It shouldn't be based on some rumours and information obtained by special services through some kind of eavesdropping, some conversations and things like that."
He noted that even in the US, "there are experts who believe that the evidence presented by the administration doesn't look convincing, and they don't exclude the possibility that the opposition conducted a premeditated provocative action trying to give their sponsors a pretext for military intervention."
He compared the evidence presented by Washington to false data used by the Bush administration about weapons of mass destruction to justify the 2003 invasion of Iraq.
He said he "doesn't exclude" backing the use of force against Syria at the United Nations if there is objective evidence proving that Assad's regime used chemical weapons against its people. But he strongly warned Washington against launching military action without UN approval, saying it would represent an aggression.
He said it was "too early" to talk about what Russia would do if the US attacked Syria. "We have our ideas about what we will do and how we will do it in case the situation develops toward the use of force or otherwise," he said. "We have our plans."