The White House on Monday warned Syria that further use of chemical weapons or chlorine-laden barrel bombs could bring US military retaliation.
Broadening its warning to Syrian President Bashar al-Assad, White House spokesman Sean Spicer indicated that such attacks were unacceptable.
"If you gas a baby or drop a barrel bomb onto innocent people, you will see a response from this president," Spicer said.
A second US official clarified that Spicer was referring to crude bombs that have sometimes been laced with industrial chlorine.
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Barrel bombs more broadly are crude munitions notorious for causing indiscriminate casualties and are used frequently during the Syrian war, according to experts and rights groups.
Assad denies his forces use the weapon.
Trump last week ordered missile strikes against an air field in Syria that US intelligence believes was used to carry out an attack with the chemical agent sarin.
The White House also doubled down on its rhetoric on the need for Syria's leader to step down.
"You can't imagine a stable and peaceful Syria with Assad in charge," said Spicer.