VIENNA — The head of the U.N. nuclear test ban treaty organization says arch-enemies Iran and Israel are “the closest” of the eight holdout nations to ratifying the treaty and assuring the world they will never conduct a nuclear test explosion.

Lassina Zerbo said this week that having Iran and Israel ratify together would “certainly” lead to Egypt’s ratification, and pave the way for a nuclear test-free zone in the Middle East.