Eleven nations attending the G20 summit in Russia have called for a clear message to be sent to Syria that the use of chemical weapons cannot be repeated.
The United States, Britain, France, Saudi Arabia and Japan said the use of chemical weapons anywhere, diminishes the security of people everywhere.
They would support strong action by the United Nations Security Council, but said the world cannot wait for endless failed processes.
At the end of the summit, President Barack Obama said there was a "unanimous" view that chemical weapons had been used in Syria.
He argued that action was required even when the Security Council was paralysed, as an international consensus against the use of chemical weapons had to be upheld.
But President Vladimir Putin of Russia said on Friday most leaders in attendance opposed military action against Syria.
The US government accuses President Bashar al-Assad's forces of killing 1429 people by poison gas in Damascus on 21 August. Mr Assad has blamed rebels for the attack.
The BBC says a report by UN weapons inspectors is not due to be made public until the week beginning 15 September - possibly even later.
China and Russia refuse to agree to a draft UN Security Council resolution against Syria. They insist any military action without the UN would be illegal.