The Philippine coast guard has opened a new monitoring base on a remote island occupied by Filipino forces in the disputed South China Sea as Manila ramps up efforts to counter China’s increasingly aggressive actions in the strategic waterway.

THITU ISLAND, South China Sea (AP) — The Philippines inaugurated a new coast guard monitoring base Friday on an island occupied by Filipino forces in the disputed South China Sea and plans to expand joint patrols with the United States and Australia to counter China’s “pure bullying” in the strategic waterway, a Philippine security official said.

High-seas faceoffs between Chinese and Philippine ships have intensified this year in the contested waters, fueling fears of a larger conflict that could involve the United States. The U.S. has repeatedly warned that it’s obligated to defend the Philippines, its oldest treaty ally in Asia, if Filipino forces come under an armed attack, including in the South China Sea.