United States Vice-President Joe Biden has arrived in Tokyo as part of a regional tour that is now expected to see China's new Air Defence Zone in the East China Sea become a major topic of discussion.
The trip, which also takes in South Korea and China, was meant to focus on economic issues and other areas of cooperation, Radio New Zealand's Washington correspondent reports.
China's neighbours have strongly protested against the decision to establish the zone which includes a set of islands currently administered by Japan but which are also claimed by Beijing.
Senior US administration officials say Mr Biden won't be delivering a formal diplomatic protest about the new defence zone, but will use the opportunity to speak directly with Chinese leaders about the move and voice Washington's concerns while he holds bilateral talks with President Xi Jinping and Premier Li Keqiang.
China has now begun patrol flights in the zone which the US fears may lead to miscalculations or a flare-up of violence.
In Japan, Mr Biden will have a working dinner with Prime Minister Shinzo Abe, as well as meet with lawmakers and in South Korea he will receive a briefing on security on the Korean peninsular and deliver a speech at a university.