Tokyo and Manila have significantly deepened military ties in recent years, with both joining a security partnership with Washington, and Japan supplying patrol boats and radio gear to the Philippines.

The Philippines and China have engaged in frequent clashes in the contested South China Sea, which Beijing claims in nearly its entirety despite an international ruling that its assertion has no legal basis.

At a joint briefing Thursday in Manila, Japanese Foreign Minister Toshimitsu Motegi said the new Acquisition and Cross-Servicing Agreement showed security cooperation between the two countries was "rapidly expanding".

Funds provided to the Philippines under Japan's Official Security Assistance programme -- valued at more than $20 million since 2023 -- were also being funneled into infrastructure for the first time, he added.

"This is the first infrastructure project under Japan's OSA program, and we will construct boathouses and slipways for rigid hull inflatable boats," Motegi said of the OSA funding.

Tokyo has been a key financer of Manila's efforts to modernise its South China Sea patrol craft as well as maritime surveillance systems.

Philippine Foreign Minister Theresa Lazaro said Thursday that the new resupply deal would "enhance our mutual military interoperability and readiness" while building off the previously signed visiting forces agreement.

Japan regularly joins the Philippines in bilateral and multilateral maritime drills in the South China Sea, and last year sent a contingent to the annual Balikatan military exercises conducted by US and Philippine forces.