Russian President Vladimir Putin has challenged the US to present to the UN evidence that Syria attacked rebels with chemical weapons near Damascus.
Mr Putin said it would be "utter nonsense" for Syria's government to provoke opponents with such attacks.
US President Barack Obama says he is considering military action against Syria after intelligence reports that 1,429 people were killed on 21 August.
UN weapons inspectors have left Syria after gathering evidence for four days.
They crossed into neighbouring Lebanon. They are due to go to the headquarters of the Organisation for the Prevention of Chemical Weapons in the Netherlands.
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.
'Trump card'
The inspectors' departure from Syria removes both a practical and a political obstacle to the launch of US-led military action, correspondents say.
The BBC's Jeremy Bowen in Damascus says people are worried and are making preparations.
They do not know what Mr Obama means by a limited attack and what consequences it will have for them, he adds.
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 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."
"So I'm convinced that is nothing more than a provocation by those who want to drag other countries into the Syrian conflict."
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He 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.
The main findings of the released unclassified summary of the US evidence state that:
the attack killed 1,429 people, including 426 children
Syrian military chemical weapons personnel were operating in the area in the three days before the attack
Satellite evidence shows rockets launched from government-held areas 90 minutes before first report of chemical attack
100 videos attributed to the attack show symptoms consistent with exposure to nerve agent
Communications were intercepted involving a senior Damascus official who "confirmed chemical weapons were used" and was concerned about UN inspectors obtaining evidence
'Completely unexpected'
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.
Forces which could be used against Syria:
• Four US destroyers - USS Gravely, USS Ramage, USS Barry and USS Mahan - are in the eastern Mediterranean, equipped with cruise missiles. The missiles can also be fired from submarines, but the US Navy does not reveal their locations
• Airbases at Incirlik and Izmir in Turkey, and in Jordan, could be used to carry out strikes
• Two aircraft carriers - USS Nimitz and USS Harry S Truman are in the wider region
• French aircraft carrier Charles de Gaulle is currently in Toulon in the western Mediterranean
• French Raffale and Mirage aircraft can also operate from Al-Dhahra airbase in the UAE
Link & Videos:
http://www.bbc.co.uk/news/world-middle-east-23911833
