The United States has issued 271 sanctions in response to Syrian president Bashar Assad's alleged use of chemical weapons.
It is one of the largest sanction actions in US history.
The government said on Monday that it issued sanctions against 271 employees of Syria's Scientific Studies and Research Centre, the Syrian government agency responsible for developing and producing non-conventional weapons.
The action was announced in a statement by the Treasury Department, and Treasury Security Steve Mnuchin simultaneously briefed reporters at the White House.
The new sanctions are the latest US response to Mr Assad's alleged use of chemical weapons, most recently in rebel-held northern Idlib, in an attack that killed more than 80 civilians.
The US retaliated earlier this month by launching missiles against a Syrian airfield.