WASHINGTON — The Trump administration on Monday said it was imposing sanctions on 271 employees of the Syrian government agency that produces chemical weapons and ballistic missiles, blacklisting them from travel and financial transactions in the wake of a sarin attack on civilians this month.

The sanctions on members of President Bashar al-Assad’s Scientific Studies and Research Center more than doubles the number of Syrian individuals and entities whose property has been blocked by the United States and who are barred from financial transactions with American people or companies. It seeks to punish those behind this month’s chemical weapons attacks and previous ones carried out by Mr. Assad’s government, senior administration officials said, and to deter others who are contemplating similar actions.

“The United States is sending a strong message with this action that we will hold the entire Assad regime accountable for these blatant human rights violations in order to deter the spread of these types of barbaric chemical weapons,” Steven T. Mnuchin, the secretary of the Treasury, said in a statement. “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.”

It was the second time the United States government has imposed sanctions on Syrians for the government’s use of chemical weapons. The Treasury Department blacklisted 18 Syrians in January after an investigation by the Organization for the Prohibition of Chemical Weapons, the international body that polices chemical weapons, determined that the government had been responsible for three chlorine gas attacks.

Syria agreed in a 2013 agreement brokered by Russia to destroy its chemical weapons arsenal and get rid of material that could be used to resume the manufacture of such weapons.

But American officials have said that this month’s attack, in Khan Sheikhoun, indicated that the Assad government still had the capacity to make and use chemical weapons.

On Monday, one official said that assault and at least one other this month suggested that Syria had an ongoing chemical weapons program and called into question declarations the government had made to the contrary.

In a report issued by the National Security Council this month that included a declassified account of the Khan Shiekhoun attack, the White House said that United States intelligence information had indicated that “personnel historically associated with Syria’s chemical weapons program” were at Shayrat airfield in March and on the day of the attack preparing for the sarin assault.

That airfield is believed to have been used by Syrian government warplanes to carry out the attack. President Trump ordered an airstrike on the airfield days later.

An official declined to say whether any of those figures were part of the group singled out on Monday, citing the need to protect intelligence sources and methods, but asserted that those being blacklisted were believed to be responsible for attacks.