The UN Security Council on Friday adopted a US-drafted resolution condemning the use of chlorine in Syria and threatening measures if chemicals are used in future attacks.
The resolution was approved by 14 of the 15 council members including Russia, Syria's ally, but Venezuela abstained.
"Today this council makes crystal clear that the use of chlorine as a chemical weapon is no less an evil than the use of any other chemical as a weapon," US Ambassador Samantha Power told the council.
While the measure does not single out the Damascus regime over the use of chlorine, Western powers have made clear that the evidence points to attacks being carried out by President Bashar al-Assad's forces.
Venezuela's Ambassador Rafael Ramirez said his country would not support the resolution as no blame was assigned over the use of chlorine in reports by the OPCW chemical weapons watchdog.
"An investigation should first be concluded in order to determine the responsibility of those who perpetrated such an abominable act," said Ramirez.
The resolution states that the Security Council "decides in the event of future non-compliance... to impose measures under chapter 7" of the UN charter, which provides for sanctions and possibly military force.
The measure "condemns in the strongest terms any use of any toxic chemical, such as chlorine, as a weapon in the Syrian Arab Republic."
Russia's envoy Vitaly Churkin said measures under chapter 7 could not be decided unless there is proof of chemical weapons used by either side in the conflict.
A report by the OPCW chemical watchdog in January concluded "with a high degree of confidence" that chlorine gas had been used in attacks on three villages in Syria last year.
At least 13 people died in the attacks that were carried out from April to August, according to the report by the Hague-based Organization for the Prohibition of Chemical Weapons.
While the OPCW did not attribute responsibility for the chlorine attacks, it cited 32 witnesses who saw or heard the sound of helicopters as bombs struck and 29 who smelled chlorine. Only the Syrian regime has helicopters.
"Despite having acceded to the Chemical Weapons Convention, the Assad regime has again demonstrated its brutality by turning to chlorine as another barbaric weapon in its arsenal against the Syrian people," Power told the council.
After an August 2013 sarin attack outside Damascus that much of the international community blamed on Assad's government, the regime agreed to turn over its chemical arsenal.
But Syria did not have to declare its stockpile of chlorine -- a toxic agent that can be considered a chemical weapon -- as part of a disarmament deal agreed in 2013 because it is widely used for commercial and domestic purposes.
The Assad regime and the rebels have accused each other of using chemical agents, including chlorine, in the nearly four-year war that has killed more than 210,000 people.