(Bloomberg) -- Ukrainian firefighters have been battling a brush fire for three days near Chernobyl, the site of the world’s worst nuclear plant disaster, as a warmer-than-normal winter left acres of dried grass and shrubbery vulnerable within the forested exclusion zone that isolates the radioactive remains.

Police investigators are probing whether the fire, which is burning about 70 kilometers (43 miles) from the lead-shrouded facility, was caused by arson. The blaze so far has charred 20 hectares (49 acres) of land north of the Kyiv region, according to the state Emergency Services Monday.

More than 100 firefighters were working in the area, which has been fenced off for decades because of radioactive materials that were spewed across the countryside during the 1986 explosion.

Radiation levels are within normal readings, the service said, though there have been concerns for years that fires within the exclusion zone may cause radioactivity to be released into the atmosphere from smoke.

Fires have broken out in the Chernobyl area in past years during bouts of dry weather, without threat to the local population.

©2020 Bloomberg L.P.