Hundreds of firefighters backed by aircraft have been battling several forest fires around Chernobyl since last week. They managed to contain the initial blazes, but new fires are now raging close to the decommissioned plant.
Volodymyr Demchuk of Ukraine's state Emergencies Service insisted that the situation is under control.
“There is no threat to the Chernobyl nuclear power plant, waste fuel storage or other critical facilities,” he said.
The emergencies service said radiation levels in the capital, Kyiv, about 100 kilometers (60 miles) south of the plant, were within norms.
Activists warned, however, that the blazes were getting dangerously close to waste storage facilities.
Yaroslav Yemelyanenko, a member of the public council under the state agency in charge of the closed zone around the plant, said one fire was raging within 2 kilometers (about 1.2 miles) from one of the radioactive waste depots.
“The situation is critical,” he said on Facebook.
Last week, officials said they tracked down a person suspected of triggering the blaze by setting dry grass on fire in the area. The 27-year-old man said he burned grass “for fun” and then failed to extinguish the fire when the wind caused it to expand quickly.
On Monday, police said that another local resident burned waste and accidentally set dry grass ablaze, triggering another devastating forest fire. They said he failed to report the fire to the authorities.
The 2,600-square-kilometer (1,000-square-mile) Chernobyl Exclusion Zone was established after the April 1986 disaster at the plant that sent a cloud of radioactive fallout over much of Europe. The zone is largely unpopulated, although about 200 people have remained despite orders to leave.
Blazes in the area have been a regular occurrence. They often start when residents set dry grass on fire in the early spring — a widespread practice in Ukraine, Russia and some other ex-Soviet nations that often leads to devastating forest fires.