Former prime ministers Junichiro Koizumi and Naoto Kan called on the European Union on Thursday to pursue a path toward zero nuclear power, with the bloc planning to designate it as a form of "green" energy in achieving net-zero emissions by midcentury.

Both Koizumi and Kan were proponents of nuclear power generation while in office, but they have become prominent antinuclear voices in Japan since the 2011 Fukushima disaster triggered by a massive earthquake and tsunami. Kan was prime minister when the disaster struck northeastern Japan.

"As a result of the 2011 nuclear accident at the Fukushima No. 1 (plant), we've learned nuclear power was not safe, cheap and clean energy," said Koizumi, a reformer who held office from 2001 to 2006, during a press conference at the Foreign Correspondents' Club of Japan.