US defense officials reported Tuesday that the Pentagon had observed new activity "associated with chemical weapons" at a Syrian aircraft hangar from which a previous chemical weapons attack on civilians is believed to have originated, Fox News reported.

The hangar is located at the Shayrat Air Base outside the city of Homs, and is in the same airbase which the US fired 59 Tomahawk cruise missiles at in early April.

“We have seen activity at Shayrat Airfield . . . associated with chemical weapons,” Capt. Jeff Davis said.

The nature of the activity was not revealed.

The report of activity at the base comes hours after US President Donald Trump warned that the regime of Syrian President Bashar Al-Assad was preparing to launch another chemical weapons attack on civilians.

According to a statement by White House Press Secretary Sean Spicer, US intelligence agencies have evidence suggesting the Syrian government is preparing for a large-scale chemical attack, similar to the strike near the city of Idlib in April which left dozens dead and hundreds more with serious injuries.

“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,” Spicer said.

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

The White House warned Assad that a new chemical weapons attack would not go unpunished.

“If… Mr. Assad conducts another mass murder attack using chemical weapons, he and his military will pay a heavy price,” said Spicer.”