The defense officials emphasized that military options are ready to present to Trump and that the intelligence could become more specific at any time.
One factor US intelligence is trying to determine is the role the Russians are playing in this effort -- chemical weapons use has been condemned by the Kremlin, but if Assad proceeds, it may demonstrate he is trying to publicly show independence from Moscow, the officials added, according to CNN.
Two other US military officials said that Russians visited the Shayrat airbase Tuesday. One of the officials said they visited a former munitions storage facility used by Russia, and the US military thinks it is "highly likely" the Russians also inspected a one-time chemical weapons shelter.
Currently, the aircraft carrier USS George H.W. Bush, along with two destroyers and two cruisers, are in the eastern Mediterranean Sea maintaining routine patrol positions.
The destroyers and cruisers could fire Tomahawk missiles without putting pilots in manned aircraft at risk.
The US claims that it 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.
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.