The Foreign Ministry unofficially complained about a U.N. report on the Fukushima disaster that was released immediately after the March 2011 earthquake and tsunami because it described the crisis-hit Fukushima No. 1 nuclear plant as "not under control," sources said Wednesday.

At the time, a series of hydrogen explosions had ripped apart two of the plant's six containment buildings because Tokyo Electric Power Co. had lost all electric power and was unable to cool the reactor fuel, which was melting.

In making the protest, the Foreign Ministry said the expression used in the report was too strong, the sources said, and implied that the government was underestimating the scale of the disaster, which involved core meltdowns in reactors 1, 2 and 3.