The Pentagon believes the Syrian regime likely has additional chemical weapons stocks at the airfield struck by US missiles last week, but these were deliberately left untouched, an official said Monday.

US intelligence experts assess Syrian President Bashar Assad’s military is probably hoarding the weapons in munitions depots at Shayrat airfield near Homs in central Syria, the US military’s Central Command spokesman Col. John Thomas said.

President Donald Trump ordered a massive military strike on the air base last week, in retaliation for a “barbaric” chemical attack he blamed on Assad.

“We suspected there was a significant probability there could be other chemical weapons which would be ready to go, weaponized in those facilities, and so we didn’t strike those,” Thomas told reporters.

The chemical stocks were left untouched because the Pentagon did not want to risk unintentionally sending a plume of toxic gas across parts of Syria.

Though the United States is confident Assad is stockpiling chemical weapons, intelligence analysts are not certain what these are.

Under a 2013 Moscow-brokered deal, Assad was supposed to have dismantled Syria’s chemical weapons arsenal and ship it to Russia.

The Pentagon has said it is sure Assad unleashed a chemical attack on April 4 that killed at least 87 civilians in the rebel-held Syrian town of Khan Sheikhun.

“Our advice was to make sure we didn’t inflict any greater damage by touching any of the chemical weapons in the area,” Thomas added.

“We were trying to degrade their capability to launch aircraft and to load them up with chemical weapons.”

The Pentagon says the strike destroyed more than 20 Syrian jets but the military has come under criticism for not targeting Shayrat’s runways, amid reports regime planes were again using the base hours after the attack by 59 Tomahawk cruise missiles.

Thomas said the runways were deliberately avoided because the US was trying to draw a clear line that its military action was in response to the suspected chemical attack, and not signal a willingness to get more involved in Syria’s brutal civil war.

US forces gave Moscow a heads up shortly before Friday’s strike, as Russian personnel and equipment were based at Shayrat under Russia’s ongoing military intervention to prop up Assad.