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 programme in 2013, and said the world must find a way to stop it.
US 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 emphasised that the US was seeking a new way to hold chemical weapons-users accountable and wanted co-operation from Russia, Assad's patron, in pressuring him to end the attacks.
Raising the alarm about the continued threat, US 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 Assad's forces are using the same chemicals - chlorine and sarin - but in more sophisticated ways, potentially to evade international accountability by making the origins of attacks harder to trace.
Barrel bombs used earlier in the war to disperse chemicals indiscriminately, for example, have been replaced by ground-launched munitions, officials said.
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.
Assad's government has denied using chemical weapons. Syria's chief ally, Russia, has claimed that the reports are false attempts to pressure Syria's government or provocations perpetrated by opposition groups.
Syria and Russia have dismissed the conclusions of the Joint Investigative Mission, an expert body set up by the UN and Organisation for the Prohibition of Chemical Weapons, that Assad's government used chlorine gas in 2014 and 2015, and sarin in April 2017.
Late in 2017, Russia used its UN Security Council veto to prevent the investigative body from being renewed, arguing it had been discredited.
That led the US and other nations to accuse Moscow of covering for chemical use by Assad's forces.
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