KYIV (Reuters) - A Russian attack overnight damaged St. Sophia Cathedral in Kyiv's historic centre, one of Ukraine's most cherished monuments, an action denounced by President Volodymyr Zelenskiy as "unacceptable and catastrophic."

Zelenskiy said the attack caused part of the facade to collapse on the 11th-century cathedral, a designated UNESCO World Heritage Site.

"For all people who truly know history and are not strangers to Christianity, even the threat of damage to or the destruction of St. Sophia is an absolutely unacceptable thing, catastrophic," Zelenskiy said in his nightly video address.

"But not for Russia. Mad with Shaheds (Iranian-designed drones) and the red button. And catastrophes are precisely the meaning of their existence. They produce nothing and will leave nothing else behind."

Culture Minister Mykola Tochytskyi said Russia had "struck at the very heart of our identity again," calling the cathedral "the soul of all Ukraine."

Tochytskyi said a blast wave damaged the cornice on the main apse of the landmark. Pieces of white plaster crumbled to the ground with a gap visible in a section of the cornice, Reuters video from the scene showed.

This is the first time since the start of the war that the cathedral has been damaged, first deputy director general of the site Vadym Kyrylenko told reporters. Russian drones flying close to the ground present a threat amid continuous air attacks on the capital.

"As our security guards say, sometimes (drones) almost touch the crosses on the bell tower 76 metres above the ground," he said.

The cathedral was added to UNESCO's World Heritage list in 1990 for its architectural importance. The United Nations' cultural body describes the white cathedral and monastery complex with green roofs and golden domes as a symbol of the "new Constantinople" created in the region.

Kyrylenko reported no critical damage and said the site will be inspected by a specialized institute and repaired.

More than a year after Russia's invasion in February 2022, UNESCO's World Heritage Committee placed the cathedral on the list of World Heritage in Danger "due to the threat of destruction the Russian offensive poses" to the monument and integrity of its ancient interiors, mosaics and frescoes.

The site was also vulnerable to shockwaves, it said.

"It is not only protected by our state, it is protected by the whole world. It is the heritage of the whole world," Kyrylenko said.

(Reporting by Vlad Smilianets and Anastasiia Malenko; Editing by Alexandra Hudson, Ron Popeski and Rod Nickel)