Russian President Vladimir Putin has dismissed US claims that Syria's regime used chemical weapons, describing them as "utter nonsense".
Mr Putin challenged Washington to present the evidence behind its claims to the United Nations Security Council.
US President Barack Obama has said he is considering military action against Syria based on intelligence reports.
The Russia leader's remarks came after UN chemical weapons inspectors ended their visit to Syria.
They crossed into neighbouring Lebanon after four days of inspections, including investigations of what happened in the Damascus suburbs on 21
Hundreds of people including children were killed in the suspected chemical weapons attacks, which the US says was carried out by the Syrian
Syria said the US claim was "full of lies", blaming rebels for the attacks.
The inspectors' departure from Syria removes both a practical and a political obstacle to the launch of US-led military action, says the BBC's Kevin
Connolly in Lebanon.
But speaking to journalists in the Russian far-eastern city of Vladivostok, Mr Putin urged Mr Obama - as a Nobel Peace Prize laureate - to think about
future victims in Syria before using force.
He said it was ridiculous to suggest the Syrian government was to blame for the 21 August attack.
"Syrian government troops are on the offensive and have surrounded the opposition in several regions," he said.
In these conditions, to give a trump card to those who are calling for a military intervention is utter nonsense."
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".
Syrian President Bashar al-Assad has said his country will defend itself against any Western "aggression".