BEIJING - China will reject and will never acknowledge the arbitration initiated by the Philippines because it is illegal and invalid no matter what it will be, said a Chinese Foreign Ministry spokesman on Friday.

Chinese Foreign Ministry spokesman Hong Lei made the remarks at a regular press briefing in Beijing on Friday in response to the reports that a tribunal set up at the request of the Philippines is likely to make a final arbitration in May or June.

"Those who expect that the arbitration could compel China to yield or make it an accomplished fact are doomed to be disillusioned. The arbitration is illegal and invalid whatever it will be. China will reject and will never acknowledge it," said Hong.

"China is firm in its determination to safeguard its sovereignty and maritime rights and interests. At the same time, we are also firm to safeguard the integrity and authority of the international law and the United Nations Convention on the Law of the Sea," Hong added.

China claims almost all of the energy-rich waters of the South China Sea, through which more than $5 trillion of maritime trade passes each year. The Philippines, Brunei, Vietnam, Malaysia and Taiwan have overlapping claims.

China's increasingly assertive moves in the waters, including building artificial islands and airports, have rattled nerves around the world, with the Group of Seven (G7) advanced economies warning last month they opposed provocation there.

G7 leaders meet for a summit in Japan later this month.

Ouyang Yujing, Director-General of Chinese Foreign Ministry's Department of Boundary and Ocean Affairs, said he had noticed recent criticism of China coming from outside the region.

"Of course we're willing to take on board constructive comments and criticism by the relevant countries," Ouyang told a news briefing.

"But if they are aimed at putting pressure on China or blackening its name, then you can view it like a spring, which has an applied force and a counterforce. The more the pressure, the greater the reaction," he said.

China has been stepping up its rhetoric ahead of a ruling expected in a few weeks by the Permanent Court of Arbitration in The Hague on a case the Philippines has brought against China's claims in the South China Sea.

U.S. officials have expressed concern the ruling could prompt China to declare an air defense identification zone, as it did over the East China Sea in 2013. China has neither confirmed nor denied it could do that.

The ruling is widely expected to favor the Philippines and risks significantly raising regional tensions because China rejects the court's authority to hear the case, even though it is a signatory of the U.N. Convention on the Law of the Sea under which it is being heard

Ouyang said China had studied the Philippines' case and decided that it was ultimately about sovereignty and maritime delineation, and China was within its rights not to participate.

Three previous international treaties - in 1898, 1900 and 1930 - have already fixed the Philippines' boundaries, Ouyang said. According to those treaties, features such as the Spratlys and Scarborough Shoal are clearly Chinese, he said.

The Philippines began "illegally occupying" Chinese islands from the 1960s, Ouyang said. (Reporting by Ben Blanchard; Editing by Paul Tait)