“If Japan is attacked, we will fight World War III. We will go in and protect them with our lives and with our treasure,” Trump said during an interview on Fox Business Network with anchor Maria Bartiromo. “But if we are attacked, Japan doesn’t have to help us at all. They can watch on a Sony television, the attack."
The president has considered pulling out of the defense pact in private, Bloomberg News reported earlier this week, but that would have a significant impact on U.S. influence in Asia and leave the island nation of Japan, surrounded by nuclear threats on all sides, to fend for itself.
The White House did not respond to a request for comment.
A senior Japanese official said Tuesday that the White House had denied that the Bloomberg report was accurate.
"There is no such talk as is mentioned in the report. We have confirmed with the U.S. president that it is inconsistent with the American government's position," said Chief Cabinet Secretary Yoshihide Suga.
"We asked about this pact to the White House, and they totally denied such a fact and said such a report is not based on fact," a Japanese official told ABC News.
While Trump did not tell reporters he would tear up the treaty, his criticism seems to undermine the White House's unequivocal denial.
The president's comments come just a month after he was treated as a special state guest in Japan met with the new emperor, attended lavish dinners and had a VIP seat at Japan's sumo wrestling tournament. While at the G20, Trump is expected to again meet with Japanese Prime Minister Shinzo Abe and discuss trade and regional geopolitical concerns, like North Korea.
But Japan wasn't the only country the president chastised ahead of his G20 trip. He also said European countries were abusing the U.S. and treat it "worse than China." He then went on to suggest an EU leader "hates the United States."
"There's a woman in Europe -- I won't mention her name -- she's actually considered to take Jean Claude's place -- she hates the United States perhaps worse than any person I've ever met. What she does to our country. She is suing all of our companies."
He went on to say the United States is propping NATO up and claimed that NATO Secretary General Jens Stoltenberg said that "'If it wasn't for President Trump we won't have NATO.'"
Trump added that he believes Canada is also taking advantage of the U.S.
"We were being taken advantage of by Canada nobody knows that -- 'O Canada,' beautiful song -- they charge 300% tariff for a little thing called agricultural products," he said.
While in Osaka, Trump will also be meeting with China’s Xi Jinping, Russia’s Vladimir Putin, Saudi Crown Prince Mohammed bin Salman, Japanese Prime Minister Shinzo Abe. Later, the president will be meeting with South Korean President Moon Jae-in when he makes a visit to Seoul, South Korea.
ABC News's Conor Finnegan contributed to this report.