Secretary of Defense James Mattis said Wednesday that the Bashar al-Assad regime in Syria has taken President Donald Trump’s warning against launching another chemical attack seriously.

“They didn’t [launch a chemical attack]. It appears they took the warning seriously,” Mattis told reporters aboard a U.S. military aircraft destined for Belgium.

Mattis’s remarks come just days after the Trump administration announced it had warned al-Assad not to use chemical weapons, since U.S. intelligence suggested the brutal regime was preparing another chemical attack against its own people.

“The United States has identified potential preparations for another chemical weapons attack by the Assad regime that would likely result in the mass murder of civilians, including innocent children,” the White House statement said Monday.