Two Japanese destroyers and one of the Philippines’ newly-acquired warships began historic naval exercises in the flashpoint South China Sea, also called the West Philippine Sea by Manila, on Tuesday, showcasing a deepening alliance aimed at countering a rising China.

The daylong war games, the first bilateral naval exercises between the former World War II enemies, took place less than 300 kilometers from a Philippine-claimed shoal now under Chinese control.

Although the Philippine navy declined to say exactly where the exercises would take place, it said the vessels would sail into the South China Sea from the former US Subic Bay naval base, about 270 kilometers southeast of Scarborough Shoal.

A Navy spokesman said the exercises were the first bilateral war games between the two nations.

He said one of the main drills would see an AW 109 helicopter from the BRP Ramon Alcaraz, a frigate acquired from the United States in 2012, flying to one of the Japanese destroyers when the three vessels meet at sea.

“It would be naive for anyone to think this is just an ordinary joint exercise in the light of some assertive actions by China in the South China Sea,” Wilfrido Villacorta, an international relations lecturer at the Manila-based De La Salle University, told AFP.

He described this as a “natural reaction” by the Philippines after recent “provocations.”

Villacorta cited in particular China’s recent flurry of reclamation activities on reefs in the Philippine-claimed Spratlys archipelago, turning them into islands capable of hosting significant military outposts.

The Spratly Islands are about 800 kilometers from Subic Bay.

Philippine authorities insisted the exercises were merely focused on building military capabilities, but security analysts said they were clearly a signal to China over bitter maritime territorial disputes.

“First they demonstrate that China’s Pacific neighbors are beginning to balance against China,” Professor Michael Tkacik, a foreign policy expert at the Texas-based Stephen F. Austin State University, told AFP.

“Japan, the Philippines, Vietnam, and assorted other states are threatened by China’s behavior, even as far away as India. Thus, the Philippines and Japan are jointly making an important statement about how seriously they view China’s actions.”

China has caused deep concern regionally in recent years as it has become more aggressive in staking its claims to the South China Sea and Japanese-claimed islands in the East China Sea.

China insists it has sovereign rights to nearly all of the South China Sea.

However the Philippines, Vietnam, Malaysia and Brunei have competing claims to parts of the sea, which is vital to the global shipping industry and is believed to contain huge deposits of fossil fuels.