Monkeys near the stricken Fukushima nuclear power plant have lower blood cell counts than cousins living further away, possibly because of radiation exposure, a study said Thursday.

A Japanese research team wrote in the journal Nature Scientific Reports that although they could not prove the link, the blood levels "might likely be the result of exposure to some form of radioactive material".

Fewer blood cells could make the monkeys more prone to disease, they said, and "may suggest that the immune system has been compromised to some extent".

The team had compared white and red blood cell levels in macaques living in a forest area of Fukushima City, 70 kilometres (43 miles) from the nuclear plant, with that of 31 monkeys living 400 km away in the Shimokita Peninsula.

"Compared with Shimokita monkeys, Fukushima monkeys had significantly low white and red blood cell counts," said the researchers.

The study sought to examine the health effects of long-term radioactive exposure on wild Japanese macaques following the massive earthquake and nuclear meltdown at Fukushima in March 2011.

Such data from non-human primates, our closest relatives, could contribute to knowledge about the health effects of radiation exposure on humans, the team said.

But some commentators criticised the research method.

Jim Smith, environmental science professor at the University of Portsmouth in Britain, said the dosage inferred in the study was unlikely to have had a significant effect on the monkeys' blood cell count.

"I think it much more likely that the apparently low blood cell counts in the Fukushima monkeys are caused by something other than radiation."

Geraldine Thomas, a professor of molecular pathology at Imperial College London, added the radiation doses would have been less than a person would receive on a flight from London to Tokyo.

The blood cell count may be caused by other factors such as a new diet or other environmental changes brought on by the tsunami, she said.