The Ukrainian air force said that Russia had launched more than 100 drones across the country overnight -- including attack drones -- targeting northern regions of the country where the Chernobyl power plant lies.

"Last night, a Russian attack drone with a high-explosive warhead struck the cover protecting the world from radiation at the destroyed 4th power unit of the Chernobyl Nuclear Power Plant," Zelensky said in a social media post.

The International Atomic Energy Agency also reported an "explosion" at the site, and said "radiation levels inside and outside remain normal and stable."

The agency, which has had a team deployed on the site since the early stages of Russia's invasion of Ukraine, published images apparently showing the drone on fire after crashing into the covering.

In 1986, a reactor at Chernobyl exploded during a botched safety test, resulting in the world's worst nuclear accident that sent clouds of radiation across much of Europe and forced tens of thousands of people to evacuate.

Soviet authorities initially tried to cover up and then play down the disaster.

Eventually a massive concrete and steel cover called a sarcophagus was built over the reactor, to contain the radiation.

"The only country in the world that attacks such sites, occupies nuclear power plants, and wages war without any regard for the consequences is today's Russia," Zelensky added in his statement.

There was no immediate response from Russia.