Tens of thousands of demonstrators held antinuclear energy rallies in Tokyo, Osaka and U.S. cities Friday over the government's decision to restart the first idled reactors since the Fukushima No. 1 meltdowns.

Fukushima Prefecture residents also staged events on the sidelines of a U.N. Conference on Sustainable Development in Rio de Janeiro, joining citizens' groups at home and abroad calling for a nuclear-free world.

In a further development, a group in Niigata Prefecture on Saturday began collecting signatures for an ordinance to hold a referendum on whether to allow a restart of Tokyo Electric Power Co.'s Kashiwazaki-Kariwa nuclear plant, the world's largest atomic energy complex.