The Trump administration on Monday imposed financial sanctions on 271 named employees of a Syrian research center it indicated was responsible for developing and producing sarin used to kill dozens of people in the April 4 chemical weapons attack by the government of President Bashar al-Assad.

The sanctions, imposed by the Treasury Department’s Office of Foreign Assets Control, freeze all money the employees may have in U.S. financial institutions and discourage other international banks from dealing with them.

“The United States is sending a strong message with this action that 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,” Treasury Secretary Steven Mnuchin said in announcing the measure.

Those named were targeted “because they have expertise in chemistry and related fields or have worked in support of chemical weapons programs since at least 2012,” Mnuchin said.

It was unclear what effect the new sanctions would have on those targeted. All are listed only as working for Syria’s Scientific Studies and Research Center, which itself was sanctioned — along with any person deemed to be involved with its chemical weapons activity — in an executive order signed by President George W. Bush in 2005. Additional sanctions were imposed on the center and affiliated organizations by Treasury in 2007.

Although none of those named is known to have assets in this country, the sanctioning of what appear to be mid-level, previously anonymous employees could have the effect of undermining confidence in the government. Those whose names have surfaced in relation to chemical weapons attacks and other alleged war crimes are more likely to be cited in any postwar investigations.

The sanctions are a second round of punishment by the administration for the chemical attack. On April 6, the United States launched 59 cruise missiles against the Syrian airfield it said was the base from which the chemical airstrikes originated.

Following a sarin attack in September 2013, in which hundreds of civilians were killed in a Damascus suburb, President Barack Obama unsuccessfully sought congressional approval to launch a military strike on the Syrian government. The Obama administration later negotiated an agreement with Russia that led to international removal of what were said to be all of Assad’s chemical weapons stocks.

Since then, the government has repeatedly been found to use bombs laden with chlorine, and international inspectors have discovered traces of sarin and other chemical weapons in some locations. But the April attack was the first time since 2013 that the Organization for the Prohibition of Chemical Weapons cited “incontrovertible” evidence that “victims were exposed to sarin or a sarin-like substance.”

The Scientific Studies and Research Center, established decades ago to advance and coordinate scientific activities in Syria, is officially unaffiliated with the government but has long been assumed to be the site of chemical weapons research and development for the Syrian military.

According to a French intelligence dossier published in 2013, a branch of the center “composed only of Alawite military personnel . . . distinguished by a high level of loyalty to the regime” is responsible for producing toxic agents for military use. Alawites are members of a branch of Shiite Islam to which Assad belongs.