"All those confirmed to have been involved in the use of chemical weapons in Syria must be held accountable," Toner stated.
The comment came after the Thursday release of the fourth report of the Joint Investigative Mechanism (JIM) expert panel, established by the UN Security Council to conduct an investigation into nine instances of chemical weapons use in Syria in 2014 and 2015.
The latest JIM report claimed that the government of Syrian President Bashar Assad has "systematically and repeatedly" used chemical weapons in the country.
Russian Foreign Ministry spokeswoman Maria Zakharova said Thursday the accusations lacked convincing facts.
On August 24, the OPCW released the results of a joint probe into chemical weapons attacks in Syria in 2014 and 2015 accusing the Syrian government of two attacks and the Islamic State jihadist group (outlawed in Russia and many other states) of one attack.