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

The US 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.

Some of the people blacklisted had worked on Syria's chemical weapons programme for more than five years, the Treasury Department said. The sanction orders US 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.

“These sweeping sanctions target the scientific support centre for Syrian dictator Bashar al-Assad's horrific chemical weapons attack on innocent civilian men, women, and children,” US Treasury Secretary Steven Mnuchin.

US authorities, he said, would “relentlessly pursue and shut down the financial networks of all individuals involved with the production of chemical weapons used to commit these atrocities.”

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The sanctions listings are the latest action taken by the Trump Administration in response to the 4 April chemical attack on Khan Sheikhoun that US authorities say killed nearly 90 people, including children. The United States says Mr Assad's forces carried out the attack, while Mr Assad has said the attack is a fabrication.

Earlier this month, the United States launched dozens of missiles against a Syrian air base the Pentagon says was used to launch the chemical attack.

President George W Bush first placed sanctions against the SSRC in 2005, accusing it of producing weapons of mass destruction.

Although the Syrian government promotes the SSRC as a civilian research centre, “its activities focus substantively on the development of biological and chemical weapons,” U.S. officials said.

During the Obama administration - in July 2016 - the United States sanctioned people and companies for supporting the SSRC, and on 12 January the US Treasury sanctioned six SSRC officials it said were linked to SSRC branches affiliated with chemical weapons logistics or research.