President Donald Trump on Monday backed the Japanese prime minister's interest in using his country's good relations with Iran to help broker a possible dialogue between the US and its nemesis in West Asia.

Trump, who has said he's open to having a dialogue with Iran, has sought to downplay fears of military conflict, but the Iranians have said they have no interest in communicating with the White House.

Trump commented during a day that opened with the high pageantry of his meeting with Japan's emperor but quickly gave way to deliberations over thorny global issues, including North Korea, trade tensions with his Japanese host and the escalating friction between the US and Iran.

“I know that the prime minister and Japan have a very good relationship with Iran so we’ll see what happens,” he said while meeting with Shinzo Abe in Tokyo.

“The prime minister’s already spoken to me about that and I do believe that Iran would like to talk. And if they'd like to talk, we’d like to talk also. We'll see what happens... nobody wants to see terrible things happen, especially me.”

Trump has imposed tough new sanctions on Iran, which are crippling its economy. Late last week, he announced the deployment of 1,500 US troops to the region amid the tensions. The US earlier deployed an aircraft carrier and B-52 bombers to the Persian Gulf in response to the intelligence of Iranian threats to US interests in the region.

Trump and Abe held talks after the US President became the first world leader to meet Japan’s new emperor, Naruhito, who ascended to the throne on May 1.

Trump’s “state call” opened with handshakes and greetings from Naruhito, and his wife, Empress Masako. As he approached the emperor, Trump said: “How are you? Thank you very much.” The first lady told the empress: “Nice to meet you.”

The president, who is on a four-day state visit, was the centre of attention at a grand outdoor welcome ceremony at Japan’s Imperial Palace, where he took a solo walk down red carpets, reviewing Japanese troops as the guest of honour.

Trump said he had a good feeling that the nuclear standoff with North Korea will be resolved.

“I may be right, I may be wrong. But I feel that we’ve come a long way. There's been no rocket testing, there's been no nuclear testing,” he said.