Beijing is facing heightened challenges to its vast territorial claims over the South China Sea, as major powers continue to send warships and aircraft to the contested waters.

Military operations in the disputed waterway have added to friction between China and the United States, as well as with Britain and Japan, observers say, leaving Southeast Asian nations with claims to the area caught in the middle.

In the latest challenge, US guided-missile destroyer the USS Decatur on Sunday passed through waters off the disputed Spratly Islands, sailing within 12 nautical miles of the Gaven and Johnson reefs during a 10-hour patrol.

Relations between China and the US are already strained amid an escalating trade war, with the two sides imposing tit-for-tat tariffs on each other’s imports. After the US warship patrol, it was revealed that Beijing had called off security talks planned for October between US Secretary of Defence James Mattis and Chinese Defence Minister Wei Fenghe.

… “It’s not only the US presence that matters these days. If anything, you’ll notice that other external powers have ramped up their military presence in the South China Sea,” said Collin Koh, a maritime security expert at Nanyang Technological University in Singapore. “I think suffice to say, at least some if not all Asean countries have already been sandwiched in between.”