MANILA, Philippines (AP) — The Philippines says a United Nations arbitration tribunal has convened in The Hague to look into a case it lodged to question the legality of China’s massive territorial claims in the South China Sea.

Department of Foreign Affairs spokesman Raul Hernandez told a news conference Tuesday that the five-member tribunal under the U.N. Convention on the Law of the Sea convened last week in the Netherlands and approved a set of rules to look into the legal challenge the Philippines launched against Beijing in January.

The Philippines says that China’s claim over virtually the entire South China Sea, including its seizure of several islets and reefs, is illegal and violates UNCLOS, the 1982 U.N. convention which sets territorial limits for coastal states.