According to Reuters, Secretary of Defense James Mattis said on Wednesday that a warning from the White House to Syrian President Bashar al-Assad averted a chemical attack like the one that occurred in April against the Syrian rebel-held town in the Idlib province.
The warning issued on Monday said that Assad and his military "will pay a heavy price" should Assad's forces carry out a chemical attack.
"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," read the White House's statement.
"The activities are similar to preparations the regime made before its April 4, 2017, chemical weapons attack," the statement said. "As we have previously stated, the United States is in Syria to eliminate the Islamic State of Iraq and Syria. If, however, Mr. Assad conducts another mass murder attack using chemical weapons, he and his military will pay a heavy price."
U.S. intelligence reported that Syrian forces were preparing for a second chemical attack at Syria's Shayrat airfield, but the attack never took place.
"It appears that they took the warning seriously," Mattis said on Wednesday to reporters flying with him to Brussels for a NATO defense ministries meeting. "They didn't do it."
Mattis was asked if Assad has called off any plans for a chemical weapons attack completely, to which the defense secretary replied "I think you better ask Assad about that."
U.S. Ambassador to the United Nations Nikki Haley told the House Foreign Affairs Committee on Wednesday that the White House's warning to Assad sent the message to Syria and its allies, Iran and Russia, "that this was something we were not going to put up with."
"So I would like to think that the president saved many innocent men, women, and children," said Haley.
Reuters reported, however, that the intelligence that prompted the warning from the White House was "far from conclusive," according to an unnamed U.S. official familiar with the intelligence report.
"It did not come close to saying that a chemical weapons attack was coming," the official said.
According to Reuters, the intelligence consisted of a Syrian warplane being seen moving into a Shayrat airbase hanger thought to contain chemical weapons.
"I think that Assad's chemical program goes far beyond one airfield," Mattis said.
Russia also responded on Wednesday. Russian Foreign Minister Sergey Lavrov told a news conference in the city of Krasnodar that if the U.S. should act with force against Syria then Moscow will respond.
"We will react with dignity, in proportion to the real situation that may take place," Lavrov said.