At least six people are reported to have been killed in the US missile strikes early on Friday.
Syria's ally Russia accused the US of encouraging "terrorists" with its unilateral actions.
"I'm disappointed in that response," said US Secretary of State Rex Tillerson.
"It indicates their continued support for the Assad regime and, in particular, their continued support for a regime that carries out these type of horrendous attacks on their own people.
"So I find it very disappointing, but, sadly, I have to tell you, not all that surprising," he added.