Ukraine has lost control of Chernobyl after it was seized by Russian troops, a presidential adviser has said.
Ukrainian authorities do not know the current condition of the Chernobyl nuclear plant, Myhailo Podolyak told the Associated Press.
However, the Mirror reports that local news outlets have suggested staff have been taken as hostages at the site.
Earlier reports suggested that a battle had broken out near the remains of the nuclear power plant, which is around 60 miles from Kyiv, the capital of Ukraine.
As Moscow seizes the site of the nuclear disaster, experts have suggested it is a key location as soldiers are now able to march directly into Ukraine's capital city.
Follow the latest on the situation in Ukraine on our live blog
Mr Podoliak, adviser to the head of the president’s office, warned: "After a fierce battle, our control over the Chernobyl site has been lost.
"The condition of the facilities of the former Chernobyl nuclear power plant is unknown. This is one of the most serious problems in Europe today.
"It is impossible to say that the Chernobyl nuclear power plant is safe.
"This is one of the most serious threats to Europe today. Knowing the habits of the Russians, they are probably already preparing provocative things at the Chernobyl nuclear power plant.
"Either they will use the damage received by the facilities during the attack to blame Ukraine for this, or they will damage these undoubtedly most dangerous facilities themselves."
Russian soldiers are said to have attacked the radioactive area from the side of Belarus before engaging in combat with local forces.
Videos from the scene of the conflict show Russian tanks stationed outside an administration building east of the nuclear plant.
Ukrainian President, Volodymy Zelenskyy, said Russia declared war on all of Europe by storming into Chernobyl.
He put on Twitter: "Russian occupation forces are trying to seize the #Chornobyl_NPP.
"Our defenders are giving their lives so that the tragedy of 1986 will not be repeated. Reported this to @SwedishPM. This is a declaration of war against the whole of Europe."
Chernobyl was the site of one of the world's worst nuclear disasters which, in 1986, sent clouds of nuclear material all across Europe.
