A US Navy warship has sailed past one of China's artificial islands in the South China Sea in a move that drew an angry reaction from Beijing.
China's foreign ministry said authorities monitored and warned the USS Lassen as it entered what China claims as a 12-mile (20km) territorial limit around Subi Reef in the Spratly Islands archipelago, where the Philippines has competing claims.
In a statement on its website, the ministry said: "The actions of the US warship have threatened China's sovereignty and security interests, jeopardised the safety of personnel and facilities on the reefs, and damaged regional peace and stability.
"The Chinese side expresses its strong dissatisfaction and resolute opposition."
The move fits the US policy of pushing back against China's growing assertiveness in the South China Sea.
The Philippines, a US ally, welcomed the move as a way of helping maintain "a balance of power".
China has accelerated the creation of new outposts since 2013 by piling sand atop reefs and atolls, then adding buildings, ports and airstrips big enough to handle bombers and fighter jets - activities seen as an attempt to change the territorial status quo by changing the geography.
Navy officials said the sail-past was necessary to assert the US position that China's man-made islands cannot be considered sovereign territory with the right to surrounding territorial waters.
International law permits military vessels the right of "innocent passage" in transiting other country's seas without notification.
China's foreign ministry, however, has described the ship's actions as illegal.
The US says it does not take a position on sovereignty over the South China Sea but insists on freedom of navigation and overflight.
About 30% of global trade passes through the South China Sea, which also has rich fishing grounds and a potential wealth of undersea mineral deposits.
China says it respects the right of navigation but has never specified the exact legal status of its maritime claims.
It says virtually all of the South China Sea belongs to it, while Brunei, Malaysia, the Philippines, Taiwan and Vietnam claim either parts or all of it.