Investigators from the United Nations and the Organization for the Prohibition of Chemical Weapons (OPCW) have blamed a sarin nerve gas massacre in the Syrian town of Khan Sheikhoun on Bashar al-Assad's regime.
More than 87 people died on April 4 when sarin gas projectiles were fired into Khan Sheikhoun, which is a rebel-held town in northwestern Idlib province.
Images of dead and dying victims, including young children, in the aftermath of the attack provoked global outrage and a US cruise missile strike on the regime air base of Shayrat.
The report supports the initial findings by the US, France and Britain that a Syrian military plane dropped a bomb with sarin on Khan Sheikhoun.
Syria and Russia, its close ally, have denied any attack and have strongly criticized the Joint Investigative Mechanism, known as the JIM, which was established by the UN and OPCW to determine responsibility for chemical weapons attacks in Syria.
"The panel is confident that the Syrian Arab Republic is responsible for the release of sarin at Khan Sheikhun on 4 April 2017," the report, seen by news agencies, said.
Responding to the report, US Ambassador Nikki Haley said: "Today's report confirms what we have long known to be true. Time and again, we see independent confirmation of chemical weapons use by the Assad regime."
Clearly referring to Russia, she said: "In spite of these independent reports, we still see some countries trying to protect the regime. That must end now."
The Security Council should make it clear that "the use of chemical weapons by anyone will not be tolerated," Haley added.