If necessary, the Trump administration is prepared to take military action against Syrian government forces to deter the use of chemical weapons, senior U.S. officials said on Thursday.
Washington is concerned forces loyal to Syrian President Bashar Assad may be developing new methods to deliver such weapons, the officials added.
Pro-regime forces have continued occasional use of chemical weapons in smaller amounts since a deadly attack last April that drew a U.S. missile strike on a Syrian air base, the officials told reporters in a briefing.
If the international community does not act quickly to step up pressure on Assad, Syria's chemical weapons could spread beyond Syria and possibly even to the United States, one of the officials said, speaking on condition of anonymity. "It will spread if we don't do something," the official warned.
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Last month, the U.S. signaled an open-ended military presence in Syria as part of a broader strategy to pave the way diplomatically for Assad's eventual departure.
U.S. Secretary of State Rex Tillerson called for "patience" on the Syrian leader's departure – the clearest indication yet of an acknowledgment that Russia and Iran have bolstered Assad and that he is unlikely to leave power immediately.
Tillerson's speech came less than a week after Turkey, Russia and Iran aggressively condemned a reported plan for the U.S. to create a new force of Kurdish militants to patrol the Syria-Turkey border – a plan the Pentagon has denied.