An increase in thyroid cancer among children is unlikely after the disaster at the Fukushima No 1 nuclear plant four years ago, but it remains unclear exactly how much radiation children in the vicinity were exposed to, International Atomic Energy Agency said in a new report.

Increased thyroid cancer is generally the leading health concern after exposure to nuclear radiation, but that may not be the case after the three reactor meltdowns at the Tokyo Electric Power Co. plant in March 2011, the Vienna-based watchdog said in the report, which was released Monday.

"Because the reported thyroid doses attributable to the accident were generally low, an increase in childhood thyroid cancer attributable to the accident is unlikely," the report says.