Japanese officials failed to implement international nuclear-safety standards designed to mitigate damage from tsunamis and earthquakes at the stricken Fukushima Daiichi plant that triggered Japan's nuclear crisis, a United Nations nuclear-agency report said.

The report, to be presented in Vienna on Monday at a ministerial-level meeting of the U.N.'s International Atomic Energy Agency and its 151 member states, is the most definitive outside review to date of Japan's nuclear accident and subsequent handling. Its findings are...