"It will spread if we don't do something", the official warned.
Such allegations were timed to undermine the efforts to resolve the Syrian war through a peaceful settlement between the Syrians without foreign interventions, it noted.
President Donald Trump has not ruled out additional military action to deter attacks or punish Assad, administration officials said earlier this week, although they did not suggest any action was imminent.
The foreign ministry's denial came a day after U.S. Defense Secretary James MattisJames Norman MattisTrump goes dark on Russian Federation and the real threat to our State of the Union The Hill's 12:30 Report Report: Mattis considering personal cellphone ban at Pentagon MORE accused the government of Syrian President Bashar Assad of repeatedly using chlorine gas to attack rebel-held parts of Syria.
Last month, activists claimed the Syrian forces used chlorine in an attack on the rebel-held Eastern Ghouta countryside of Damascus, causing 21 people to suffer from breathing difficulties.
The Syrian government denied the accusations, saying it's rebels who mounted the attack to frame the government and draw in a military action from the United States.
The US officials claimed that Syrian armed forces have "evolved" their chemical weapons and occasionally used them in smaller amounts since 2017. Unlike sarin, chlorine gas is relatively easy to produce and is not banned by the Chemical Weapons Convention. "I don't have the evidence;" of the Syrian regime's use of sarin gas but that "groups on the ground, NGOs, fighters on the ground have said that sarin has been used". Mattis hinted at such action on Friday, referencing a US missile strike on a Syrian military airfield a year ago. Mattis told reporters that sarin gas is something that has been weaponized and that "we are even more concerned about the possibility of sarin use, the likelihood of sarin use, and we're looking for the evidence".