A US Navy ship has sailed close to artificial islands built by China in the disputed waters of the South China Sea, US defence officials have said.
Guided-missile destroyer USS Lassen breached the 12-nautical mile zone China claims around Subi and Mischief reefs in the Spratly archipelago.
The freedom of navigation operation represents a serious challenge to China's territorial claims.
The foreign ministry in Beijing condemned it as "illegal".
In a statement, ministry spokesman Lu Kang described the operation as a "threat to China's sovereignty", adding that Beijing would "resolutely respond to any country's deliberately provocative actions".