TOKYO, Aug. 8 - United Nations Secretary-General Antonio Guterres on Monday urged countries with nuclear weapons to stick to their no-first-use commitment of their atomic arsenals, warning that the nuclear arms race has returned amid growing international tension.

“This is the moment … to ask the nuclear-armed countries to commit to the principle of non-first-use and to commit to not use and not threaten the non-nuclear countries,” Guterres said at a news conference in Tokyo, two days after he visited Hiroshima to commemorate victims of the Aug. 6, 1945, atomic bombing.