The head of the Organisation for Economic Cooperation and Development urged Japan on Tuesday to resume nuclear electricity generation despite public opposition.
Nuclear energy has become controversial since the meltdowns at Tokyo Electric Power Company's Fukushima Daiichi plant following the tsunami in March last year, the world's worst atomic disaster in a quarter of a century.
Since then, no power plant that has gone offline for regular safety checks has been permitted to restart, and only one of Japan's 50 reactors remains in action -- but is due to be shut down on May 5.
Nuclear power supplied almost a third of the country's electricity needs before the disaster and OECD Secretary General Angel Gurria said on a visit to Japan: "You cannot substitute 30 percent of installed capacity overnight."
Gurria said he understood a more cautious public view of nuclear power in the wake of the Fukushima disaster, but he hoped Japan would continue "to have an important nuclear capacity to generate electricity".
Kyodo News quoted him as saying: "As a condition of growth policy, you have to have sufficient sources of energy to fuel the economy, households, companies, and infrastructure."
Supporters say without nuclear power, energy-hungry and resource-poor Japan cannot continue to function normally, but critics point to continuing efficiencies that have allowed it to shrug off previous warnings of shortages.