US President Donald Trump on Thursday startled Japan's Prime Minister (PM) by referring to the 1941 attack on Pearl Harbor, in a remark that was intended to be light-hearted but was likely to cause unease in a country that is now a close ally of the United States (US).

Speaking in a notably cordial meeting with PM Sanae Takaichi, Trump explained to reporters why he had not informed allies before the US and Israel carried out military action against Iran on February 28, news agency AFP reported.