The United States on Monday blacklisted 271 employees of a Syrian government agency it said was responsible for developing chemical weapons, weeks after a poison gas attack killed scores of people in a rebel-held province in Syria.

The U.S. Treasury Department sanctioned 271 employees of Syria’s Scientific Studies and Research Center (SSRC), an agency that Washington says develops chemical weapons for the government of Bashar al-Assad, the Treasury said in a statement.

Some of the people blacklisted had worked on Syria’s chemical weapons program for more than five years, the Treasury Department said. The sanction orders U.S. banks to freeze the assets of any employees named, and bans American companies from conducting business with them.

Those designated were “highly educated” individuals likely to be able to travel outside of Syria and use the international financial system even if they may not have assets abroad, administration officials said during a conference call with reporters.

“These sweeping sanctions target the scientific support center for Syrian dictator Bashar al-Assad’s horrific chemical weapons attack on innocent civilian men, women, and children,” U.S. Treasury Secretary Steven Mnuchin said in a statement.

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