TOKYO — Japan took a decisive step on Tuesday toward ending a two-year freeze on the use of nuclear power, as an electric utility restarted one of the dozens of reactors in the country that were taken offline after meltdowns at a plant in Fukushima in 2011.

The reactor at the Sendai Nuclear Power Plant, in Kagoshima prefecture, is the first to return to service since government regulators introduced upgraded safety standards in 2013. Most of Japan’s 48 operable commercial nuclear reactors were shut down soon after the Fukushima accident, and none have operated since 2013.

The issue of whether Japan should again join the ranks of nations that use nuclear power is a highly contentious one here. The government of Prime Minister Shinzo Abe supports restarting idled reactors that meet the new enhanced safety standards, arguing that Japan’s economy depends on the low-cost power they provide.

Japan has few domestic energy sources, and the country imports virtually all the fossil fuels it uses to power its cars, homes and factories. Electricity prices in Japan have increased by 20 percent or more since the Fukushima disaster, squeezing households and businesses.