The U.S. deployed two warships Wednesday in a disputed South China Sea shoal where two Chinese ships collided earlier in the week while trying to drive away a smaller Philippine ship in a high-seas accident that raised alarms about maritime safety.

China’s military announced that it had monitored and “drove away” a US Navy destroyer that sailed close to the Scarborough Shoal in the South China Sea. This shoal is a small group of rocks and reefs but has become one of the most hotly contested areas in the region.

A US Navy guided-missile destroyer performed a so-called Freedom of Navigation operation (FONOP) near disputed Scarborough Shoal in the South China Sea on Wednesday, just two days after two Chinese military vessels collided while chasing a Philippine Coast Guard ship in nearby waters.