Foreign Affairs Secretary Alberto del Rosario said Wednesday that any new construction by China in waters that are also claimed by the Philippines is a clear violation of a 2002 accord that calls for countries to exercise restraint.

The Philippine military has reported that Chinese ships were seen unloading building materials and erecting posts in the vicinity of the Spratly islands’ Iroquois Bank, which is 125 miles (200 kilometers) from southwestern Palawan province.

China, the Philippines and four other nations claim the potentially oil-rich Spratlys, which straddle busy shipping lanes.