Ukraine’s President Volodymyr Zelensky announced Friday that an armed Russian drone struck and pierced the exterior protective shell over the site of the 1986 Chernobyl nuclear disaster. 

Moscow denied responsibility for the incident, claiming it was a “false flag” attack from Ukraine. The International Atomic Energy Agency said that radiation levels outside the containment building remained normal.

Fighting from the Ukraine–Russia war has occasionally come close to sensitive nuclear sites, notably Ukraine’s Zaporizhzhia power plant, which has been struck by drones several times.

The incident comes as American officials at the Munich Security Conference meet with Ukrainian and European partners about brokering the peace deal President Donald Trump has announced as a priority for his administration.