A number of hot spots, or areas where radiation levels are significantly higher than average, have been found at key Olympic venues in Japan's Fukushima Prefecture, with the Summer Olympics just four months away.

The environmental group Greenpeace held simultaneous news conferences in Seoul and Tokyo on Monday, where it unveiled results on the amount of radiation measured at key spots in the prefecture from October 16 to November 5 last year.

The report shows zero-point-48 microsievert(μsv) of radiation measured on a road near Azuma Baseball Stadium where some baseball and softball events will take place during the Tokyo Games.

The figure is more than double the zero-point-23 level of radiation in the atmosphere targeted by the Japanese government through decontamination operations, which involved removing the soil in contaminated areas.

Greenpeace said hot spots are still being found in the area, including in downtown Fukushima, despite Japan's efforts. The group suspected that Typhoon Hagibis, which swept through the country last October, may be to blame for the failure in decontamination.