More than 50 missiles were filed from US Navy destroyers in the eastern Mediterranean, striking several targets, a US official said, speaking on condition of anonymity.
Further details on the target and the results of the strikes were not immediately known.
US President Donald Trump is expected to address the nation shortly, CNN reported.
Earlier, US Secretary of State Rex Tillerson said Syrian leader Bashar al-Assad should have no role in a future Syria.
His comments signalled a sudden shift in policy by the new US administration.
