MANILA, Philippines—China is turning the West Philippine Sea (South China Sea) into “one country’s lake,” Foreign Secretary Albert del Rosario said on Tuesday, pressing Manila’s effort to roll back Beijing’s expansive claims in the strategic waterway.

Speaking before an experts’ roundtable on maritime security in Brussels, Belgium, Del Rosario said China’s assertion of ownership over almost all of the sea could restrict freedom of navigation in sea-lanes critical to global trade.