The US president referenced the WWII attack to defend the decision not to notify allies of the strikes against Iran

US President Donald Trump joked about the 1941 attack on Pearl Harbor in front of a visibly uncomfortable Japanese Prime Minister Sanae Takaichi, as he defended his decision not to warn allies before striking Iran.

Speaking to reporters in the Oval Office on Thursday, Trump was pressed on the lack of advance notice to Washington's partners before the US and Israel launched massive strikes on Iran last month, a decision that upended energy markets and led to a major Middle East escalation.

"We didn't tell anybody about it because we wanted surprise," the president explained, before turning to Takaichi and saying: "Who knows better about surprise than Japan? Why didn't you tell me about Pearl Harbor?"

Takaichi maintained her composure and did not comment, but was apparently taken aback by the remarks.

Trump was referring to Japan's 1941 attack on Pearl Harbor, which killed more than 2,400 Americans and led to the US entering World War II. While Japan initially achieved some success in the Pacific, the war ended with the US dropping nuclear bombs on Hiroshima and Nagasaki, the country's unconditional surrender, and American occupation until 1952.

Trump went on to praise Takaichi as "a spectacular woman," adding that they discussed Japan's support for the US in the Iran war. "They are really stepping up to the plate," he added, without providing details.

A Wall Street Journal report on Thursday said America's "longstanding allies weren't informed of the battle plans until hours before the first attack," adding that it was particularly "infuriating" for the Gulf countries, which came under retaliatory Iranian strikes.

Trump's comments come amid a widening rift between the US and European NATO members over the Iran conflict. Trump warned his European NATO counterparts that the bloc could face a "very bad future" unless they step up to help unblock the Strait of Hormuz.

European leaders have pushed back. German Defense Minister Boris Pistorius said, "this is not our war." EU foreign policy chief Kaja Kallas noted that there is "no appetite" among member states to become actively involved in the conflict.

Trump replied that NATO is "making a very foolish mistake," adding that the Iran war turned out to be a "great test" on whether the bloc "would ever be there for us."