Ukrainian authorities reported a recent spike in radiation levels in the restricted zone around Chernobyl, scene of the world's worst nuclear accident in 1986, caused by a forest fire.

Ukraine's head of ecological inspection service, Yegor Firsov, said on Facebook, "There is bad news - radiation is above normal in the fire's centre."

The post included a video with a Geiger counter showing radiation at 16 times above normal levels.

The fire has spread to about 100 hectares (250 acres) of forest, Firsov wrote.

Kyiv mobilised two planes, a helicopter and more than 100 firefighters to battle the blaze, which broke out on Saturday and spread over 20 hectares in a forested area near the Chernobyl power plant.

By Sunday morning, the fire was under control and no increase in radiation in the air was detected, the emergencies service said in a statement.

However, it noted increased radiation in some areas had led to "difficulties" in fighting the fire, while stressing people living nearby were not in danger.

On Monday, firefighters said they managed to put out the smaller of two fires, which engulfed about five hectares (12 acres), but the second one was still burning across an area of about 20 hectares (50 acres).

Police said they tracked down a person suspected of starting the blaze by setting fire to dry grass in the area. A 27-year old man said he burned grass "for fun" and then failed to extinguish the fire when the wind caused it to quickly spread.

The authorities said while radiation levels in the area engulfed by fires substantially exceeded normal levels, those in the capital, Kyiv, about 100km (60 miles) south, were close to normal.

Ukrainian police said they ramped up patrols in the area around the Chernobyl zone to prevent new fires.

Chernobyl polluted a large swath of Europe when its fourth reactor exploded in April 1986, with the area immediately around the power plant the worst affected.

People are not allowed to live within 30km (18 miles) of the power station.

The three other reactors at Chernobyl continued to generate electricity until the power station finally closed in 2000. A giant protective dome was put in place over the fourth reactor in 2016.