Japan's 2011 Fukushima nuclear disaster has raised the risk of thyroid cancer for people living near the plant, but no jump in cases is expected elsewhere, the WHO said Thursday.
The World Health Organisation said in a report that within a 20-kilometre (12-mile) radius of the plant, rates of thyroid cancer among women exposed to radiation as infants were expected to be up to 1.25%.
The normally expected risk of thyroid cancer over a woman's lifetime in the region is 0.75%, the UN health agency noted in a 166-page report.
Radioactive iodine released in nuclear accidents tends to accumulate in thyroid glands.
In the 1986 Chernobyl disaster in what was then Soviet Ukraine, a noticeable increase in thyroid cancer cases was detected among children in the affected area.
The risk of breast cancer among women exposed as infants, and of leukaemia among men exposed as infants, also looked set to rise, albeit to a lesser extent, the WHO said.
"The primary concern identified in this report is related to specific cancer risks linked to particular locations and demographic factors," sais Maria Neira, the WHO's director of public health and environment.
"A breakdown of data, based on age, gender and proximity to the nuclear power plant, does show a higher cancer risk for those located in the most contaminated parts. Outside these parts - even in locations inside Fukushima prefecture - no observable increases in cancer incidence are expected," Neira said in a statement.
Radiation doses from the stricken plant were not expected to cause an increase in miscarriages, stillbirths and other physical and mental conditions that could affect babies born after the accident, the WHO said.
The agency said that a in-depth analysis of the health impact of the disaster would be crucial for many years.
"The WHO report underlines the need for long-term monitoring of those who are at high risk, along with the provision of necessary medical follow-up and support services," said Neira.
A massive undersea earthquake in March 2011 sent a huge tsunami crashing into Japan's northeast, crushing whole communities and sending nuclear reactors on the coast into meltdown.
Around 19,000 people were killed by the natural disaster, but no one is officially recorded as having died as a direct result of the radiation that spewed from the crippled units in the following months.