Emperor Naruhito ascended to the throne on May 1, opening what is called the era of "Reiwa," or "beautiful harmony." Trump and first lady Melania kicked off the formal visit with greetings with Naruhito and Empress Masako.

The president, who is on a four-day state visit to Japan, was treated to a welcome ceremony full of pomp and pageantry. On a hot, sunny day, Trump stood at attention alone atop a platform before he walked along a red-carpeted route to review troops. Military bands played and Trump passed in front of a group of schoolchildren feverishly waving US and Japanese flags.

Trump later attended the Japanese state guest house for meetings and a working lunch with Japanese Prime Minister Shinzo Abe.

The first couple is also invited to a state banquet at the palace in the evening.

Trump said he and Abe "understand each other very well" and discussed Iran amid rising tension between Tehran and Washington.

He said he backed the Japanese prime minister's efforts to reopen communications with Iran over their nuclear program, with Japanese media reporting Abe is considering a visit to Tehran next month.

"Nobody wants to see terrible things happen, especially me," Trump said.

"I do believe Iran would like to talk and if they'd like to talk, we'll talk also."

Trump and Abe also discussed trade and North Korea. Trump has repeatedly criticised Japan for its chronic trade surplus with the US, threatening to slap tariffs on Japanese cars and car parts.

But he claimed on Sunday "great progress" had been made in trade talks.

"Great progress being made in our Trade Negotiations with Japan. Agriculture and beef heavily in play," Trump tweeted, having previously urged Abe to open the country's automotive and agriculture markets.

On Sunday, Trump and Abe played golf and watched a sumo wrestling match at the Ryogoku Kokugi-kan, where the president presented a special US-made trophy to rank-and-file wrestler Asanoyama, the winner of the Summer Grand Sumo Tournament in Tokyo.

With AP

Australian Associated Press