The U.S. imposed new sanctions on Syria in response to a chemical weapons attack earlier this month that Western officials have said was ordered by Syrian President Bashar Assad, Treasury Secretary Steven Mnuchin announced Monday.

The new sanctions freeze assets and prevent U.S. entities from doing business with more than 200 employees of a Syrian government agency tasked with producing non-conventional weapons.

Mnuchin said the measures show “we will not tolerate the use of chemical weapons by any actor and we intend to hold the Assad regime accountable for its unacceptable behavior.”

The sanctions follow a cruise missile strike ordered by President Trump against a Syrian airbase where the chemical attack was believed to have originated.

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The U.S. government and several Western allies say Assad’s forces killed 80 civilians with sarin, a lethal gas that painfully destroys the human nervous system. Assad’s use of the banned chemical weapon triggered international outcry, and U.S. officials promised to boost sanctions against Syria soon after.

Monday’s action, one of the largest in Treasury’s history, targets 271 employees of Syria’s Scientific Studies and Research Center (SSRC).

The affected individuals “have expertise in chemistry and related disciplines and/or have worked in support of SSRC’s chemical weapons program since at least 2012,” according to the Treasury Department.

Mnuchin said the sanctions target “the scientific support center for Syrian dictator Bashar al-Assad’s horrific chemical weapons attack.”

“We take Syria’s disregard for innocent human life very seriously, and will relentlessly pursue and shut down the financial networks of all individuals involved with the production of chemical weapons used to commit these atrocities,” Mnuchin said.

The State and Treasury Departments also targeted 18 senior regime officials and five branches of the Syrian military in January after a United Nations agency found the Assad regime responsible for deadly chlorine gas attacks in 2014 and 2015.

Updated at 2:24 p.m.