(CNN) The United States has sailed two warships past a handful of disputed islands in the South China Sea for the first time, a move that drew the ire of Beijing.

A US official told CNN that the guided-missile destroyer USS Higgins and the cruiser USS Antietam sailed within 12 miles of four of the Paracel Islands in its what the US Navy calls a "freedom of navigation operation" (FONOP), which are meant to enforce the right of free passage in international waters.

Ian Storey, senior fellow at the ISEAS Yusof Ishak Institute, told CNN it was the first time under the Obama and Trump administrations that more than one US ship had been involved in such an operation.

"It appears that the US it pursuing a harder line against China in the South China Sea ... Of course whether these will actually have any impact on China's behavior is unclear," he said.