Syria appears to be preparing a new chemical weapons attack against its citizens, the White House said Monday, warning that if the weapons are again used, the US will make the Syrian government “pay a heavy price.”

White House press secretary Sean Spicer revealed the news in a statement late Monday.

“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 activities are similar to preparations the regime made before its April 4, 2017 chemical weapons attack.

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.”

Officials at US Central Command told BuzzFeed News they have “no idea” what prompted the statement. Pentagon spokesmen did not answer calls seeking comment. Secretary of Defense James Mattis departed earlier Monday evening for a three-day trip to Germany and Belgium, and Joint Chiefs of Staff chairman Joseph Dunford was in Afghanistan.

The White House did not specify what form any US retribution would take, or what intelligence suggested that Syrian President Bashar al-Assad was preparing to once again deploy chemical weapons on his own people.

A major chemical attack against civilians in April prompted the US to launch air strikes against Syrian forces. It was the first time the US military had targeted the Syrian government since the country’s civil war began six years ago.

Graphic images of the attack’s devastation moved Trump to order the strike, he later said.

“Even beautiful babies were cruelly murdered at this very barbaric attack,” he said from his Florida club Mar-a-Lago. “No child of God should ever suffer such horror.”