Treasury Secretary Steven Mnuchin said that the US would soon impose additional sanctions on Syria, as part of a military, diplomatic and financial response to a chemical attack blamed on the regime.

"We will be announcing additional sanctions on Syria as part of our ongoing effort to stop this type of activity and emphasize how significant we view this," Mnuchin said from Trump's golf resort in Mar-a-Lago, Florida.

"We expect that they will continue to have an important effect on preventing people from doing business with them," he added, without offering more details.