China’s coastguard has seized Sandy Cay, a small sandbank in the Spratly Islands. CCTV showed officers raising the Chinese flag on the reef earlier in April, asserting control over the area, BBC reported.

In response, the Philippines, which also claims the reef, posted a similar photo of its police waving the flag and landed security guards on neighboring sandbanks. It's still unclear which sandbanks were involved.

China's "illegal presence" close to the sandbanks was denounced by the Philippine National Task Force for the West Philippine Sea, which also reported seeing seven militia vessels and a coastguard ship, according to BBC.

While China has not established permanent occupancy of Sandy Cay, the incident adds to the region's extending tensions, which have resulted in frequent clashes. The White House expressed alarm over China's actions, as the dispute continues with rival claims from many countries.