Donald Trump met with former Japanese prime minister Taro Aso in New York on Tuesday, part of the Republican's shadow diplomacy as he campaigns to return to the White House in November's elections.

Trump welcomed Aso to Trump Tower, one of the real estate magnate's properties in New York, where he is currently on trial accused of falsifying business records to cover up an affair with an adult film star.

"He is a highly respected man in Japan and beyond, somebody that I've liked and I've known," Trump said of Aso at the start of their meeting in a video posted on social media by his aides.

"We like each other and we'll be talking about Japan and the United States right now and lots of other things," he added.

When he's not in court, Trump has been talking to foreign officials and criticizing the policies of President Joe Biden, who defeated him in 2020.

In recent weeks, the Republican nominee-in-waiting has met with British Foreign Secretary David Cameron, Polish President Andrzej Duda and Hungarian Prime Minister Viktor Orban. 

A close ally of assassinated former prime minister Shinzo Abe, Aso is still considered a heavyweight in Japan's ruling Liberal Democratic Party.

During his presidency, Trump played golf with Abe, whom he described as a "good friend" at the time.

Without directly mentioning his meeting with Aso, Trump raged Tuesday about the exchange rate between the yen and the dollar -- with the dollar recently hitting a 34-year high against the Japanese currency.

"It sounds good to stupid people, but it is a disaster for our manufacturers and others," he said on Truth Social.

The Japanese government on Wednesday played down the pair's meeting as being conducted "in the capacity of one lawmaker", top government spokesman Yoshimasa Hayashi said.

"Therefore, I decline to comment on these activities, which the government is not involved in," he told reporters, echoing an earlier response by the foreign minister.

When asked if a Japanese cabinet minister could meet Trump, Hayashi said there were no plans "at this point".

This month, Japanese Prime Minister Fumio Kishida met Biden in Washington where the pair unveiled their countries' biggest-ever upgrade in defense ties.

Biden rolled out the red carpet for Kishida with a lavish dinner as he underscored Japan's importance as a key ally against Beijing in the Asia-Pacific region.

The two leaders announced plans to restructure the US military command in Japan -- aimed at making US and Japanese forces more nimble in the event of threats, such as a Chinese invasion of Taiwan.

Long-pacifist Japan is doubling its military spending as part of a security overhaul announced in 2022, which also includes acquiring counter-strike capabilities.

Hayashi was asked on Wednesday about concerns that the Japan-US alliance may be shaken if Trump wins in November.

The "strong" alliance enjoys wide support "across party lines" in the United States, he said.