Ukraine said on Saturday that firefighters have extinguished a forest fire that had burned for four days near the Chernobyl plant, scene of the world's worst nuclear accident in 1986.

The fire was completely put out "at 9:00 am on Saturday," the emergencies ministry said in a statement.

The levels of radiation were slightly elevated at the Chernobyl site, which is about 100 kilometres (62 miles) from the Ukrainian capital Kiev, it said.

The blaze came within about 20 kilometres (12 miles) of Chernobyl after breaking out Tuesday afternoon, but officials said it posed no danger to the plant and firefighters brought it under control within a day.

The area around Chernobyl was evacuated after the 1986 blast and the last reactor there was shut down in 2000 but some personnel still operate in the exclusion zone, where work is underway to build a new seal over the reactor site.

Officials gave few details of the possible cause of the fire but Interior Minister Arsen Avakov said authorities had not ruled out arson.

The fire struck just two days after Ukrainians marked 29 years since the Chernobyl nuclear disaster.