A drone armed with a warhead hit the outer protective shell of Ukraine's Chernobyl nuclear plant on Friday, damaging the structure and briefly starting a fire, in an attack Kyiv blamed on Russia.

The Kremlin denied it was responsible.

Radiation levels at the shuttered plant in the Kyiv region — site of the world's worst nuclear accident — have not increased, according to the UN's International Atomic Energy Agency, which said the strike did not breach the plant's inner containment shell.

The IAEA did not attribute blame, saying only that its team stationed at the site heard an explosion and was informed that a drone had struck the shell.

Fighting around nuclear power plants has repeatedly raised fears of a nuclear catastrophe during three years of war, particularly in a country where many vividly remember living through the 1986 Chernobyl disaster, which killed at least 30 people and spewed radioactive fallout over much of the Northern Hemisphere.

The Zaporizhzhia nuclear power plant, which is Europe’s biggest, has occasionally been hit by drones during the war without causing significant damage.

The strike came two days after US President Donald Trump upended American policy on Ukraine, saying he would meet with Russian President Vladimir Putin to discuss ending the war.

The move seemed to identify Putin as the only player that matters and looked set to sideline Ukrainian President Volodymyr Zelensky, as well as European governments, in any peace talks.

Zelensky said a Russian drone with a high-explosive warhead hit the plant's outer shell and started a fire, which had been put out.

The shell was built in 2016 over another heavy concrete containment structure, which was placed on the plant’s fourth reactor soon after the 1986 disaster.

Both shells seek to prevent radiation leaks. (AP)