China should agree to face the Philippines before a UN arbitration tribunal to avoid the long-raging territorial dispute from spilling over into a military conflict in the region, a senior US lawmaker said Tuesday.

“It is best that China joins the process so that we can move forward under international law,” Rep. Edward Royce, chairman of the US House Foreign Affairs Committee, told AP after meeting Philippine Foreign Secretary Albert del Rosario and other diplomats in Manila.

Royce reiterated Washington’s neutral stance but claimed it supports an approach “from the standpoint of diplomacy” to calm the simmering dispute.

Last week, the Philippines made a bold move when it notified China that it will challenge Beijing’s claims to virtually the entire South China Sea in a case before an arbitration tribunal under the United Nations Convention on the Law of the Sea.

“The Philippines has exhausted almost all political and diplomatic venues for a peaceful negotiated settlement of its maritime disputes with China,” Del Rosario said.

Beijing has not issued a formal response but reiterated China’s “indisputable sovereignty” over the contested region, Chinese ambassador to Manila Ma Keqing said. Beijing has also insisted on bilateral negotiations between the parties.