United States Vice president Joe Biden was due on Tuesday to visit Japan's tsunami-hit coast, where American forces helped with a large-scale relief effort, as he nears the end of his Asia tour.
Biden is the highest-ranking American official to visit the disaster zone where the massive March 11 earthquake and tsunami claimed more than 20,000 lives and sparked the ongoing Fukushima nuclear disaster.
The United States, with bases across Japan since World War II, mobilised more than 20,000 troops and some 160 aircraft in disaster relief and recovery operations after Japan's worst peace-time catastrophe.
Biden was due to visit the airport of Sendai city, which was swamped by the tsunami and where US troops using heavy equipment performed most of the clean-up effort during their wider "Operation Tomodachi" (Friend).
The quake relief effort, and US help with containing the nuclear emergency, have helped rebuild relations between Tokyo and Washington which were long strained by a dispute over a US airbase on Japan's Okinawa island.
Many people on the subtropical island have long chafed under a heavy post-war US military presence and demanded that the contentious base, the US Marine Corps Air Station Futenma, be moved off the island.
Japan's former prime minister Yukio Hatoyama stepped down last year after first promising to move the base off the island, then reneging on the pledge -- managing to anger both Washington and Okinawans in the process.
The allies have since agreed to go ahead with a planned move of the base within Okinawa, but have been forced to scrap a 2014 deadline for the shift.
The US vice president was due to meet Prime Minister Naoto Kan in the morning in Tokyo for talks that were expected to touch on the base issue and on the strength of the countries' half-century security alliance.
However, the meetings are overshadowed by the fact that Kan, under fire for his post-disaster leadership, has only days left in office before he is set to make way next week for Japan's sixth new premier in five years.
After a lunch in Tokyo, Biden was due to fly to Sendai in the afternoon and deliver a speech at the rebuilt airport before returning to Tokyo.
On Wednesday he visits the US military headquarters in Japan at the Yokota airbase west of Tokyo, where he was to deliver another speech.
Biden arrived in Tokyo Monday night after touring China and Mongolia.
He used his five-day visit to China, his first as vice president, to reassure senior leaders about the safety of US Treasuries following a historic downgrade this month of the country's top-notch credit rating.
Beijing has used the proceeds of its export machine to invest around $1.17 trillion in US Treasury bonds, making it the largest foreign holder of US debt.