The U.S. has identified "potential preparations" for another chemical weapons attack by the regime of Syrian President Bashar Assad, the White House announced in a statement Monday night.

The White House said the activities are "similar" to preparations the Assad regime made before the Syrian government's nerve gas attack on civilians in April that led President Trump to approve missile strikes against a Syrian airbase.

"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. "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."

Soon after the White House released its statement, Nikki Haley, U.S. ambassador to the United Nations, tweeted her own warning to the Syrian government, and countries that support Assad.

"Any further attacks done to the people of Syria will be blamed on Assad, but also on Russia & Iran who support him killing his own people," Haley said.

Any further attacks done to the people of Syria will be blamed on Assad, but also on Russia & Iran who support him killing his own people. — Nikki Haley (@nikkihaley) June 27, 2017

On April 6, less than three days after the Syrian government's last known chemical weapons attack, Trump ordered the launch of 59 Tomahawk cruise missiles at Al Shayrat airfield in western Syria. This was the site where the chemical weapons attack originated.

The chemical weapons attack killed more than 80 civilians.

At the time, H.R. McMaster, Trump's national security adviser, said the retaliatory missile strikes would not eliminate Assad's ability to use chemical weapons, but would degrade it.

Since the April nerve gas attack and the U.S. government's retaliation, the relationship between the two countries has worsened. Earlier this month, the U.S. shot down a Syrian warplane, the first time an American warplane has downed a manned aircraft since 1999.