U.N. Secretary General Antonio Guterres visited Washington on June 28.
He met with U.S. secretary of State Rex Tillerson.
While at the State Department a reporter asked Guterres about the warning to Syria.
On June 26 the Trump White House warned Syria not to launch any chemical attacks.
The statement said Syria would pay “a heavy price” for future chemical attacks.
Guterres responded simply. “I believe it was a serious warning, and I think serious warnings should be heard.”
According to the statement, U.S. sources saw Syrian forces engaging in activity identical to that which preceded the April 4 chemical attack by Syrian forces on civilians in a rebel-held area. About 100 civilians died, about two dozen of them children.
President Trump responded by ordering a Tomahawk missile strike on the airfield from which the chemical attack originated.
While much equipment was destroyed, the airfield was not put out of commission.
Experts speculate that the response to another chemical weapons attack could be much more significant.
The situation between Syria and the U.S. has intensified in recent months with the U.S. taking a firmer position protecting its allies in the region who are battling ISIS.
Syrian attacks on those allies led to the first downing of a Syrian jet by U.S. forces.
A U.S. Superhornet shot down a Syrian SU-22 fighter-bomber jet on June 19 after it dropped bombs near Syrian Democratic Forces (SDF) fighters south of Tabqah, Syria, about 30 miles from Raqqa.