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 US. The US 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. China has accused the US of meddling.