A Russian drone attack has hit the radiation shelter protecting Chernobyl's damaged nuclear reactor, Ukrainian President Volodymyr Zelensky has said.
The overnight strike at the nuclear plant, which is the site of the world's worst nuclear accident, caused a fire that has since been extinguished, he added. Russia has not yet commented.
As of Friday morning, radiation levels had not increased at the plant, Zelensky said.
The UN's nuclear watchdog, the International Atomic Energy Agency (IAEA), said fire safety personnel and vehicles responded within minutes of an overnight explosion. No casualties were reported, the agency added.
The IAEA, which monitors nuclear safety around the world, said radiation levels inside and outside Chernobyl remain normal and stable.
The agency remains on "high alert" after the incident, with its director general Rafael Mariano Grossi saying there is "no room for complacency".
In 1986, a catastrophic explosion at Chernobyl sent a plume of radioactive material into the air, triggering a public health emergency across Europe.
Zelensky posted footage on X appearing to show damage to the giant shield, made of concrete and steel, which covers the remains of the reactor that lost its roof in the explosion.
The shield is designed to prevent further radioactive material leaking out over the next century. It measures 275m (900ft) wide and 108m (354ft) tall and cost $1.6bn (£1.3bn) to construct.
Since 1990, Prof Jim Smith from the UK's University of Portsmouth has studied the aftermath of the nuclear disaster and, while he admits the strike was a "horrendous attack on a very important structure" he is "not concerned" about the radiation risk.
He told the BBC a thick concrete "sarcophagus" below the damaged outer shield covers radioactive particles in dust from the explosion.
A drone strike would not be strong enough to damage this protective layer, Prof Smith said.
Zelensky claimed the attack shows Russian President Vladimir Putin is "definitely not preparing for negotiations", after US President Donald Trump said Putin had agreed to begin talks to end the war in a surprise announcement this week.
"Every night, Russia carries out such attacks on Ukraine's infrastructure and cities," Zelensky said. He called for "unified pressure" to hold Moscow accountable.
Later on Friday, Zelensky will meet US Vice-President JD Vance and Secretary of State Marco Rubio for talks in Munich, with the war in Ukraine expected to dominate a major security meeting of world leaders.
The incident at Chernobyl comes after increased military activity around the Zaporizhzhia Nuclear Power Plant in southern Ukraine, the IAEA said.
In December, Ukraine and Russia accused each other of launching a drone attack on a convoy of vehicles transporting IAEA experts heading to the Zaporizhzhia plant, which is Europe's largest nuclear station.
IAEA head Rafael Grossi condemned that attack on his staff as "unacceptable", stressing that the agency was "working to prevent a nuclear accident during the military conflict".
The agency last year urged restraint when an attack on Zaporizhzhia raised the risk of a "major nuclear incident". Russia and Ukraine traded blame over the attack in August.
"I'm more concerned about Zaporizhzhia than Chernobyl," Prof Smith told the BBC.
"The reactors [at Zaporizhzhia] are currently shut down but there is more live fuel there. Chernobyl is still very radioactive, but it's not in a 'hot state' because of its age."
