Hundreds of Ukrainian firefighters are battling to control forest fires that threaten to engulf the site of the Chernobyl nuclear power plant, as environmental campaigners accuse authorities in Kiev of covering up the extent of the danger. The raging fires, said to be the largest recorded in the so-called exclusion zone – a mostly uninhabited area covering a 30-kilometre radius around the Chernobyl plant – have been burning for more than 10 days. Ukraine’s Emergency Situations Service on Monday said it was still fighting the fires, one of which is now only one kilometre from the site of what is widely considered to be the worst nuclear accident in history. The disaster sent a cloud of radioactive fallout across Europe when Chernobyl’s fourth reactor building exploded during a safety test in 1986. It led to the evacuation of the nearby town Pripyat, then home to around 50,000 people, and the creation of the 2,600-square kilometre exclusion zone on Ukraine’s northern border with Belarus. Aerial photographs taken on Monday showed a wall of flames inching closer to the reactor complex, with trees ablaze and plumes of black smoke billowing into the sky. Kiev has mobilised helicopters and more than 400 firefighters, with planes dropping tons of water on the fire. "There is no threat to the Chernobyl nuclear power plant and the storage facilities," Volodymyr Demchuk, a senior Emergency Situations Service official said late on Monday. The Emergency Situations Service said radiation levels in the exclusion zone had not changed and those in nearby Kiev, the Ukrainian capital, "did not exceed natural background levels". But a day after the fire broke out, the head of the state environmental service, Yegor Firsov, wrote on Facebook that radiation readings at the centre of the fire were higher than normal. He later withdrew the claim. And several news outlets, including <em>The New York Times</em>, have reported rising levels as the fires spread some of the radioactive material absorbed by plants in the zone since the disaster. Environmental campaigners on Monday accused the Ukrainian authorities of covering up the extent of the danger. Greenpeace Russia said the situation is much worse than the authorities have led people to believe. The fires, they say, cover an area one thousand times bigger than is officially claimed. On April 4, Ukrainian authorities said the largest blaze covered an area of 20 hectares, but Greenpeace cited satellite images showing that it was around 12,000 hectares in size at that time. "According to satellite images taken on Monday, the area of the largest fire has reached 34,400 hectares," it said, adding that a second fire, stretching across 12,600 hectares, was just one kilometre away from the defunct plant. Rashid Alimov, the head of energy projects at Greenpeace Russia, said the fires, fanned by the wind, could disperse radionuclides, atoms that emit radiation. "A fire approaching a nuclear or hazardous radiation facility is always a risk," Mr Alimov said. Yaroslav Yemelianenko, a Chernobyl tour operator, described the situation as critical. He said that the fire was rapidly expanding and had reached the abandoned city of Pripyat, two kilometres from where "the most highly active radiation waste of the whole Chernobyl zone is located", and called on officials to warn people of the danger. The fires, which follow unusually dry weather, began on April 3 in the western part of the exclusion zone and spread to nearby forests. Police say that they have identified a 27-year-old local resident who they believe deliberately started them. The exclusion zone has become a popular tourist destination and has enjoyed a surge in popularity thanks to the hit television series <em>Chernobyl</em>, which dramatised the events surrounding the nuclear disaster at reactor four. The three other reactors continued to generate electricity until the power station was closed in 2000. A giant protective dome was put in place over the fourth reactor in 2016.