The United States, Japan and the Philippines have staged joint naval drills to boost crisis readiness off a disputed South China Sea shoal as a Chinese military ship kept watch from a distance.

Mischief and Subi reefs are among the artificial islands China has used to expand its offensive capabilities in the region.

The deployment of the USS Shoup and JS Noshiro to Scarborough Shoal represents the strength of the U.S.-Japan-Philippine alliance.