The Philippines took delivery of two Japanese military surveillance aircraft to help it patrol vital sea lanes in the South China Sea, despite Manila's increasingly conciliatory stance to Beijing's claims over the disputed waters.
Japan will lease a total of five surplus Beechcraft TC-90 planes to the Philippines, according to Manila's defence secretary Delfin Lorenzana.
Philippine military chief General Eduardo Ano said the new planes would be deployed over Benham Rise and the South China Sea.
Japan's attempt to bolster defence cooperation with Manila comes at a time of heightened regional concern over China's activities in disputed waters.
"As we are faced with many security-related issues in the Asia-Pacific, including those in the South China Sea, our cooperation with the Philippines for the regional security and stability is now even more significant," Japanese Defense Minister Kenji Wakamiya said at a ceremony to hand over the planes.
Japan, which has a territorial row with China over disputed islands in the East China Sea, has worked to strengthen ties with other countries in a bid to contain its regional rival.
China claims most of the sea, including waters close to the Philippine coast, despite the claim being declared as without basis last year by a United Nations-backed tribunal.
Beijing opposed the Philippines' lease of the planes almost as soon as it was announced last year under Manila's then-president Benigno Aquino III, who took a tough stance on China's territorial ambitions.
However, Aquino's successor President Rodrigo Duterte has reversed this stance, openly courting China for trade and aid, while playing down the South China Sea dispute.
Earlier this month Duterte said he was open to sharing resources with Beijing in the flashpoint waters, saying he could not stop Beijing from building on a disputed shoal near his country's west coast, which China seized from the Philippines in 2012.
He also brushed aside concerns over Chinese survey ships that had been seen near Benham Rise -- waters east of the main Philippine island of Luzon that have been recognised by the United Nation as indisputably Philippine territory.
Parts of the South China Sea are also subject to competing claims by Brunei, Malaysia, Taiwan and Vietnam.