A US Navy destroyer navigated within 12 nautical miles of artificial islands China is building in the South China Sea, a US defense official said.

The USS Lassen sailed in waters surrounding at least one of the land formations claimed by China in the disputed Spratly Islands chain early Tuesday local time, the official told AFP.

Tensions have mounted since China transformed reefs in the area -- also claimed by several neighboring countries -- into small islands capable of supporting military facilities, a move the US says threatens freedom of navigation.

Washington has repeatedly said it does not recognize Chinese claims to territorial waters around the artificial islands.

"We are conducting routine operations in the South China Sea in accordance with international law," the official said.

"US forces operate in the Asia-Pacific region on a daily basis, including in the South China Sea."

The official stressed that these operations are "distinct from the question of sovereignty over these islands."

Beijing insists it has sovereign rights to nearly all of the South China Sea, even waters close to the coasts of other states.

The sea is a strategically vital waterway with shipping lanes through which about a third of all the world's traded oil passes, and the dispute has raised fears of clashes.

"We have been clear that we take no position on competing territorial sovereignty claims to land features in the South China Sea," the US defense official said.

"We will fly, sail, and operate anywhere in the world that international law allows."

The official insisted that freedom of navigation operations, which are global in scope, are "not directed at any specific country."

Brunei, Malaysia, the Philippines and Vietnam -- members of the Association of Southeast Asian Nations (ASEAN) -- also claim parts of the sea. Taiwan is a sixth claimant.
Source: AFP