"The sight of people being gassed and blown away by barrel bombs ensures that if we see this kind of action again, we hold open the possibility of future action," White House spokesman Sean Spicer told reporters.
If you gas a baby, if you put a barrel bomb into innocent people … you will see a response from this president.
Barrel bombs are oil drums or cylinders packed with explosives and shrapnel.
Trump ordered a cruise missile strike on Syria's Shayrat air base last week in response to what his administration and US allies say was a poison gas attack by Syria's military in which scores of civilians, including many children, died.
Spicer said later his mention of barrel bombs as a potential trigger for further action by the United States did not reflect a change in position.
"Nothing has changed in our posture," he said by email.
"The president retains the option to act in Syria against the Assad regime whenever it is in the national interest, as was determined following that government's use of chemical weapons against its own citizens. And as the president has repeatedly made clear, he will not be telegraphing his military responses."