WASHINGTON (REUTERS) - United States President Donald Trump is expected to visit Japan in May to meet the country's new emperor and then return to the country in June for a Group of 20 (G-20) gathering, a White House official said on Wednesday (Feb 20).

His first visit will likely take place from May 26 to 28, Japanese broadcaster NHK reported earlier on Wednesday, citing Japanese officials.

Mr Trump is expected to become the first foreign dignitary to meet Crown Prince Naruhito after he succeeds his father, Akihito, as emperor of Japan on May 1, NHK said.

Mr Trump will also attend the Osaka meeting of the Group of 20 largest world economies in June, the White House official said.

Mr Trump's administration has been working with the political leadership of both Japan and South Korea in advance of his summit at the end of the month with North Korea's leader Kim Jong Un, as they work to help achieve the US goal of convincing North Korea to abandon its nuclear weapons.

North Korea has threatened to strike all three nations with nuclear weapons.

Mr Trump also spoke with Japanese Prime Minister Shinzo Abe on Wednesday morning, according to the White House, and the two leaders "reaffirmed their commitment to achieving the final, fully verified denuclearisation of" North Korea and discussed Mr Trump's upcoming summit with Mr Kim.

In remarks to reporters in the Oval Office ahead of a meeting with Austrian Chancellor Sebastian Kurz, Mr Trump confirmed he spoke with Mr Abe about North Korea.

"I spoke with Prime Minister Abe of Japan about that, and we compared notes. And I think we are very much on the same wavelength," Mr Trump said.

Mr Abe has said Japan is committed to normalising diplomatic relations with North Korea and has pledged to work with China to resolve tensions on the peninsula.

The Japanese embassy in Washington did not immediately respond to requests for comment.