President Vladimir Putin has challenged the US to present to the UN evidence that Syria attacked rebels with chemical weapons near Damascus.
The Russian president said it would be “utter nonsense” for Syria’s government to provoke opponents with such attacks.
President Barack Obama says he is considering military action against Syria after intelligence reports that 1,429 people were killed on August 21.
UN weapons inspectors have left Syria after gathering evidence for four days.
They are taking their samples to the Organization for the Prevention of Chemical Weapons, in The Hague.
The samples are thought to include soil, swabs from munitions, blood and hair from the victims and, experts say, possibly even flesh from dead bodies.
The US says hundreds of children were among those killed in the suspected chemical weapons attacks, which the US says was carried out by the Syrian government.
Syria said the US claim was “full of lies”, blaming rebels for the attacks.
President Barack Obama said on Friday the US was planning a “limited, narrow” military response that would not involve “boots on the ground”.
The inspectors’ departure from Syria removes both a practical and a political obstacle to the launch of US-led military action, correspondents say.
Syrian people are worried and are making preparations.
They do not know what Barack Obama means by a limited attack and what consequences it will have for them.
Speaking to journalists in the Russian far-eastern city of Vladivostok, Vladimir Putin urged Barack Obama – as a Nobel Peace Prize laureate – to think about future victims in Syria before using force.
The Russian president said it was ridiculous to suggest the Syrian government was to blame for the attack.
“Syrian government troops are on the offensive and have surrounded the opposition in several regions,” Vladimir Putin said.
“In these conditions, to give a trump card to those who are calling for a military intervention is utter nonsense.”
“So I’m convinced that is nothing more than a provocation by those who want to drag other countries into the Syrian conflict.”
Vladimir Putin said that the US failure to present evidence to the international community was “simply disrespectful”.
“If there is evidence it should be shown. If it is not shown, then there isn’t any,” he said.
Russia – a key ally of Syria – has previously warned that “any unilateral military action bypassing the UN Security Council” would be a “direct violation of international law”.
Moscow, along with China, has vetoed two previous draft resolutions on Syria.
Vladimir Putin also expressed surprise at a vote in the British parliament on Thursday ruling out participation in military action.
“I will be honest: this was completely unexpected for me,” he said.
“This shows that in Great Britain, even if it is the USA’s main geopolitical ally in the world… there are people who are guided by national interests and common sense, and value their sovereignty.”
Meanwhile in France – seen as the main US ally since the UK vote – an opinion poll suggested that 64% opposed the use of force.
Neither France nor the US needs parliamentary approval for military action.
Syrian President Bashar al-Assad has said his country will defend itself against any Western “aggression”.