Bashar Al-Assad's air force used chemical weapons in a 2018 attack on Saraqib, the Organisation for the Prohibition of Chemical Weapons said.
Analysis: Washington is still weighing up its approach to Syria, but the power balance that Russia, Turkey and Iran have built will not be easy to change.
Book Club: Joby Warrick's new book takes a detailed look at the use of chemical weapons in Syria and the extraordinary efforts to rid the country of these dangerous materials.
In her first Security Council meeting, Linda Thomas, Washington's new UN envoy, said Russia was blocking "all efforts to pursue accountability" against the Assad regime over its chemical weapons use.
A group of Syrian chemical attack survivors and Syrian rights groups filed a criminal complaint in France.
The Syrian expert passed on information on the regime's chemical weapons programme on to the CIA.
Israeli missiles killed at least six Iran-backed fighters in Syria.
Syria's declarations on chemical weapons were criticised by UN officials and a global watchdog.
Russia and Syria have repeatedly denied the accusations of chemical weapons use, alleging that Western powers have politicised the Hague-based OPCW.
Syrian Americans have been affected by Trump's discriminatory policies and his 'Muslim ban' but many of them fear that a Biden presidency will embolden Iran in its support for Assad.