WASHINGTON — The Trump administration on Thursday accused Syrian President Bashar Assad’s government of producing and using “new kinds of weapons” to deliver deadly chemicals despite committing to abolish its program in 2013, and said the world must find a way to stop it.

President Donald Trump has not ruled out additional military action to deter attacks or punish Assad, administration officials said, although they did not suggest any action was imminent. They emphasized that the United States was seeking a new way to hold chemical weapons-users accountable and wanted cooperation from Russia, Assad’s patron, in pressuring him to end the attacks.

Raising the alarm about the continued threat, U.S. officials said it was “highly likely” that Assad kept a hidden stockpile of chemical weapons after 2013 that he failed to properly disclose. They said information gathered from recent alleged attacks also suggested that Assad retained a “continued production capacity” — also banned under the 2013 deal.

There were no indications that the Syria government, after seven years of civil war, had developed new, deadlier chemicals. Rather, the officials said they believed the weapons used to distribute the chemicals had evolved to become more sophisticated, potentially to evade international capability by making the origins of attacks harder to trace. The officials weren’t authorized to speak on the record and briefed reporters on condition of anonymity.

More recent attacks have involved both chlorine, which has nonchemical uses and is easier to acquire, and the more sophisticated chemical sarin, the officials said. They said that in recent years, Assad has also adjusted his tactics to reduce the chances that attacks will be attributed to his forces.