China and several Southeast Asian nations are currently embroiled in a territorial and maritime dispute in the South China Sea over an area that includes a cluster of resource-rich islands and important trade routes. As China’s presence in the area becomes harder to ignore, Japan has quietly begun forging security ties with Chinese geopolitical adversaries.

According to a report by Reuters, Tokyo will be involved in joint training exercises with Vietnam and the naval military of the Philippines. The two countries have been China’s biggest challengers when it comes to vocalizing their own sovereignty claims in the region. Tokyo has reportedly offered 10 coast guard boats in the area ahead of what will be the first joint naval exercises between the Philippines and Japan in upcoming months. The two countries forged a security pact in Tokyo in January that also confirmed regular meetings between vice ministers regarding defense. Additionally, Tokyo military medical professionals have offered help in advising Vietnamese submariners on avoiding decompression sickness.

Though Japan doesn’t have a vested interest in the South China Sea, it does have experience in dealing with China when it comes to disputed territories. China and Japan both lay claim to a cluster of islands in the East China Sea known as the Diaoyu (Chinese) and the Senkaku (Japanese). The islands have been a point of contention between the two governments and the problem has proliferated to also become a dispute between citizens. Though it seems like China is taking on most of Asia when it comes to its territorial claims, China’s military prowess in the region outnumbers most of its neighbors by a long shot.

Japan’s increased involvement reflects calls made by U.S. military officials earlier this year. “I think allies, partners and friends in the region will look to the Japanese more and more as a stabilizing function,” Adm. Robert Thomas, commander of the Seventh Fleet and the top U.S. naval officer in Asia, said in a separate Reuters report. “In the South China Sea, frankly, the Chinese fishing fleet, the Chinese coast guard and the [navy] overmatch their neighbors.”

China’s control over the area, in the form of dredging to erect a man-made island in the middle of the disputed Spratly Islands, overshadows attempts made by the Philippines to go to international courts in The Hague, Netherlands, to settle the dispute.

Japan’s newly introduced involvement has raised concern for China. A spokesman for China’s Foreign Ministry reportedly said that ministry officials hoped Japan would “speak and act cautiously” in regard to involving itself in South China Sea claims. China has steadfastly condemned the involvement of third-party allies, such as the United States, or groups in facilitating or weighing in on the subject.