Story highlights For now, Syria's Shayrat airbase remains under constant overhead surveillance by the US

Defense officials emphasize that military options are ready to present to Trump

Washington (CNN) The US military has ships and aircraft in place to strike Syria if ordered to do so by President Donald Trump, but so far it does not appear as if the Syrian government has made any further moves toward a chemical weapons attack, several defense officials have told CNN.

For now, Syria's Shayrat airbase remains under constant overhead surveillance by the US for further signs of whether a chemical strike may be in the works. The US recently observed the movement of an aircraft and chemical agents on a base toward possible preparation for an attack, leading the White House to issue a public warning late Monday that Syrian President Bashar al-Assad would pay a heavy price for chemical weapons use.

Earlier Wednesday, Defense Secretary James Mattis said he believes Syria has backed down.

"It appears that they took the warning seriously," Mattis told reporters during a trip to Brussels for a NATO meeting. "They didn't do it."

Nikki Haley, the US ambassador to the UN, told Congress Wednesday that Trump's warning stopped the Assad regime.

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