China is taking the highly unusual step of refusing to participate in a United Nations arbitration process over a territorial conflict with the Philippines, one of five countries challenging Beijing’s claims of ownership over the oil-rich South China Sea.

The legal dispute underscores the tough geopolitical approach China is adopting in the Pacific region. It has adopted an aggressive approach toward neighbours over a 2,000-mile stretch that also includes the East China Sea, over which it recently declared the air defence identification zone that has inflamed tensions with Japan and South Korea.

China sent its only aircraft carrier to the disputed waters off the coast of the Philippines for the first time last week, in a move Manila said raised tensions. China’s military said the carrier Liaoning will conduct drills in the area, accompanied by two destroyers and two frigates.