The Philippines is pressing ahead with an unprecedented international arbitration claim against China over contested waters in the South China Sea, despite the risk of escalating a longstanding diplomatic row with the rising power.

Manila on Sunday submitted a pleading to the body that arbitrates maritime disputes under the UN Convention on the Law of the Sea (Unclos). The so-called “memorial” will urge the tribunal to invalidate the “nine-dash line” that China includes on maps to justify its claim to almost the entire South China Sea.

Beijing is involved in maritime disputes with several neighbours, but Manila and Tokyo have been the most aggressive in challenging its claims. Last month, Benigno Aquino, the Philippines president, compared China’s increasingly assertive stance in the South China Sea to Hitler’s push for Czechoslovakian land in 1938.