US secretary of state says "it is vital for the international community to stand up and speak out" over August attack.
The US has called for a binding UN resolution on Syria's chemical weapons next week, as a senior Syrian official said the country's conflict has reached a stalemate.
John Kerry, the US secretary of state, said the "definitive" UN report had proved that the Syrian regime was behind an August chemical weapons attack.
"Now the test comes. The Security Council must be prepared to act next week," Kerry said. "It is vital for the international community to stand up and speak out."
Syria's deputy premier, meanwhile, said Damascus believed the conflict had reached a stalemate and would call for a ceasefire if long-delayed peace talks in Geneva were to take place.
"Neither the armed opposition nor the regime is capable of defeating the other side," Qadri Jamil told the British newspaper The Guardian.
When asked what his government would propose at the stalled Geneva-2 summit, he replied: "An end to external intervention, a ceasefire and the launching of a peaceful political process."