A damning report by the United Nations blames Bashar al-Assad's government for a deadly chemical weapons attack in the north west of Syria in April.
The UN report's authors have said they are "confident" sarin nerve agent was used in the attack that killed more than 80 people.
US ambassador to the UN, Nikki Haley said: "Today's report confirms what we have long known to be true".
More than 87 people died in the nerve gas attack on the town in Idlib province, with the images spurring the US to fire cruise missiles at a Syrian air base believed to be where the assault had been launched.
The report seen by AFP stated: "The panel is confident that the Syrian Arab Republic is responsible for the release of sarin at Khan Sheikhoun on April 4 2017".
Damascus denies it was behind the attack, although in September, the UN said they had evidence the Syrian air force was behind it. Syria's ally Russia says the sarin attack was most likely caused by a bomb set off directly on the ground.
Haley's statement said: "Time and again, we see independent confirmation of chemical weapons use by the Assad regime. And in spite of these independent reports, we still see some countries trying to protect the regime. That must end now.
"Ignoring the overwhelming amount of evidence in this case shows a purposeful disregard for widely agreed international norms.
"The (UN) Security Council must send a clear message that the use of chemical weapons by anyone will not be tolerated, and must fully support the work of the impartial investigators. Countries that fail to do so are no better than the dictators or terrorists who use these terrible weapons."