TOKYO — Japan will begin restarting its idled nuclear plants after new safety guidelines are in place later this year, Prime Minister Shinzo Abe said Thursday, moving to ensure a stable energy supply despite public safety concerns after the Fukushima disaster.

In a speech to Parliament, Mr. Abe pledged to restart nuclear plants that pass the tougher guidelines, which are expected to be adopted by a new independent watchdog agency, the Nuclear Regulation Authority, as early as July. He did not specify when any of the reactors might resume operation, and news reports have suggested that it might take months or even years to make the expensive upgrades needed to meet the new safety standards.

Still, by making the promise in front of the Diet, Mr. Abe indicated in the strongest way yet that he planned to move ahead with a campaign pledge to reverse his predecessor’s hopes that Japan would begin weaning itself off nuclear energy.

The speech came as the World Health Organization published a comprehensive, two-year analysis on the health risks associated with the 2011 disaster suggesting that the chance of getting certain types of cancers had increased slightly among children exposed to the highest doses of radioactivity. But the report said that there would most likely be no observable increase in cancer rates in the wider Japanese population.