Vietnamese Prime Minister Nguyen Xuan Phuc said Saturday that Japan, as a major regional power, should play a more active role in promoting the peaceful resolution of disputes involving the South China Sea.

In an interview in Hanoi with Japanese media, Phuc also said he expects Japan to make “effective” efforts to advance regional cooperation in a bid to ensure the freedom of navigation in and aviation over the contested waters.

China, which claims almost all of the South China Sea, has been aggressively pursuing its assertion, including through massive land-reclamation projects, despite objections by smaller rival claimants such as Vietnam and the Philippines.

Japan, which is not a claimant, is among countries that advocate freedom of navigation and overflight in the waters.

In his first interview with the foreign press since taking office in April, Phuc said he would visit Japan to attend in an outreach session of the Group of Seven summit on May 26-27 in Mie Prefecture.

The 61-year-old leader described bilateral ties with Japan as being in “the best-ever development stage” and expressed hope that the government would continue providing aid to improve Vietnam’s infrastructure and for boosted cooperation in areas such as climate change.

The two countries have been promoting defense cooperation, in an apparent attempt to keep China in check.

In April, two Japanese destroyers made a port call to Vietnam’s strategic Cam Ranh Bay facing the South China Sea, becoming the first Maritime Self-Defense Force vessels to visit the site.