WASHINGTON • Hours before departing on Wednesday for a global economic summit in Japan, US President Donald Trump complained about the military alliance between the two countries, criticised world leaders he will see at the gathering and unloaded on a list of domestic political foes, including a star of the United States women's soccer team.

Mr Trump's comments, during a wide-ranging Fox Business interview and on Twitter, came as he prepared to discuss a range of pressing issues at the two-day Group of 20 meeting in Osaka, including trade disagreements and escalating tensions in the Middle East.

"If Japan is attacked, we will fight World War III," Mr Trump said on Fox Business. "We will go in, and we will protect them, and we will fight with our lives and with our treasure. We will fight at all costs. But if we are attacked, Japan doesn't have to help us at all. They should watch it on a Sony television, the attack."

In the same interview, Mr Trump berated China over stalled trade talks, and falsely said China is bearing the full brunt of US tariffs imposed this year, despite the effect they are having on US consumers. "Don't play. Don't let anyone tell you that China is not paying for it. China is paying for it," he said. "We are not paying for any of it."

Mr Trump is set to meet Japanese Prime Minister Shinzo Abe today, and his comments about the military agreement could add a bit of awkwardness. He is also expected to meet Chinese President Xi Jinping on the sidelines of the gathering, and to hold a similar separate meeting with Russian President Vladimir Putin.

Mr Trump also criticised European leaders he will see at the Japan meeting, renewed a tariff threat against Europe, denounced his handpicked Federal Reserve chairman and complained that Vietnam is "almost the single worst abuser of everybody".

Mr Trump dislikes set-piece group sessions such as the G-20, whose chief value is often symbolic, and he frequently uses them to make vague and often inaccurate complaints that other countries take advantage of the US in trade and defence.

Just hours before the Group of Seven Summit in Canada in June last year, he attacked Canadian leader Justin Trudeau and French leader Emmanuel Macron, and suggested that Russia should be invited to the exclusive forum, which was designed in part to specifically exclude leaders from Moscow.

And hours after that summit, Mr Trump exploded in anger at Mr Trudeau and announced that he was withdrawing from a joint statement with the other countries.

Mr Trump also took what appeared to be another swipe at the late Senator John McCain, telling a crowd in Washington that senators who had given him a "hard time" have "gone on to greener pastures - or perhaps far less green pastures". "We had a little hard time with a couple of them, right?" Mr Trump said of Republican senators who voted against him on repealing the Affordable Care Act in 2017. "Fortunately they are gone now," he said in campaign-style remarks to a largely evangelical Christian audience at the Faith and Freedom Coalition.