US President Barack Obama wrapped up his three-day visit to Tokyo and departed for South Korea on Friday morning without a broad trade accord with the host as expected.

In a statement issued by the White House shortly before Obama left Japan, the two nations said they would continue working towards a bilateral trade deal after talks failed to reach a conclusion.

Obama and Japanese Prime Minster Shinzo Abe made a last-ditch push for the Trans-Pacific Partnerships talks at a summit on Thursday, but according to Japanese Economy Minister Akira Amari, the thorny issue of market access for agricultural products and automobiles has not been resolved.

Obama, on a state visit to Japan for the first time since Bill Clinton in April 1996, assured Japan that Washington was committed to its defense, including over islets at the heart of a row with China, but denied he had drawn a "red line" by saying his government took no side on the issue.

He also shied away from the question of whether America will intervene militarily if an armed incursion targeting the disputed islands happens.

In the joint statement, belatedly released a day after the summit, Japan and US said they back diplomatic settlements for disputes in South China Sea.

After arriving in South Korea, Obama is scheduled to hold talks with his South Korean counterpart Park Geun-hye later in the day. The four-nation Asia tour will also take him to Malaysia and the Philippines.