The Philippine government released military surveillance photos of Chinese land reclamation on a reef claimed by Manila in the South China Sea that it said showed Beijing violated a regional agreement not to escalate territorial disputes.

The aerial photographs were accompanied by a caption stating that they were obtained from “Philippine intelligence sources.” The caption said the “extensive reclamation” by China on the Johnson South Reef, called Mabini by Manila and Chigua by Beijing, was “destabilizing.”

An airstrip or a military base on the reef would boost the mobility of Beijing’s naval and air forces in the South China Sea region, far from the Chinese mainland.

The reef, part of the Spratly Islands chain, is also claimed by Vietnam, which fought a deadly naval battle against China in the area in 1988.

By Associated Press writers Jim Gomez, Christopher Bodeen, and Matthew Pennington via Yahoo! News.