The U.S. identified "potential preparations" for the use of chemical weapons that appear similar to the April 4 attack that prompted President Donald Trump to order a cruise-missile strike against Syrian military targets on April 6, according to a statement from the office of press secretary Sean Spicer.
But according to the former Assad general, the Syrian leader failed to declare large amounts of sarin precursor chemicals and other toxic materials.
In the brief statement, the White House gave no details of the purported preparations or of how they had been detected.
The White House accused the Syrian government of preparing a chemical weapons attack against rebels in that country's brutal civil war and warned Syrian President Bashar al-Assad that he will "pay a heavy price" if such an attack is carried out.More news: Erdogan rejects Arab demands; Turkish troops stay in Qatar
President Trump responded by ordering strikes against the Syrian military with Tomahawk missiles, launched by US ships in the Eastern Mediterranean against the Shayrat air base, where the USA said the planes that carried out a chemical weapons attack had originated.
The White House has provided no immediate evidence to back up its claims. United States and allied intelligence officers have identified several sites where they suspect the Assad government may be hiding newly-made chemical weapons from inspectors.
Trump previously accused the Syrian government of launching a chemical weapons attack on April 4.
The attack - which killed at least 87 people, including 30 children - escalated tensions between Washington and Russian Federation, which has advisers in Syria aiding its close ally Assad.More news: Skipper Virat Kohli steers clear of 'respected' coach Anil Kumble's departure
At the time, USA officials said the intervention was a "one-off" meant to deter future chemical weapons attacks and not an expansion of America's role in the Syrian war.
The Trump administration on Monday directly threatened Syria if it launched another chemical attack against its people.More news: US secure first win of America's Cup, trail New Zealand 4-1