Russia launched a massive overnight assault on Ukraine Monday, killing at least 11 people and setting fire to one of the Orthodox world's most sacred sites — the Dormition Cathedral at the Kyiv-Pechersk Lavra monastery.

The UNESCO World Heritage site, founded in the 11th century, holds deep spiritual significance for both Ukrainian and Russian Orthodox believers. Its golden domes and sprawling cave system house the relics of dozens of saints revered by both churches.

The attack came as G7 leaders gathered for a summit in France, where the US-Iranian peace deal was expected to dominate talks. Ukrainian President Volodymyr Zelensky urged them to give a "decisive and substantive" response.

"This is one of Russia's most serious crimes against Christian culture to date," Zelensky said on social media.

Russia's military claimed it struck military targets in Kyiv, Kharkiv, and Dnipro, and denied targeting the monastery. Moscow alleged the cathedral was hit by a Ukrainian Patriot missile — a claim Ukraine denies.

Ukraine's air force said it intercepted 50 of the 70 missiles and 582 of the 611 drones launched overnight. But the ones that got through caused devastation.

In Kyiv, five people were killed and 34 wounded. A building at the Mystetsky Arsenal National Art and Museum Complex also caught fire, Ukraine's emergency service said.

In the northeastern city of Kharkiv, five people died — rescue workers and a civil servant. A Ukrainian drone strike on the Russian city of Tula, about 200 kilometres south of Moscow, killed three more people and wounded three, regional governor Dmitry Milyaev said.

The Dormition Cathedral's roof was engulfed in flames. The cathedral had been almost completely destroyed during World War II and was only rebuilt in the 1990s. The monastery itself was at the centre of a dispute in 2022-2023, when monks from the Ukrainian branch of the Moscow church were evicted over alleged ties to Russia.

"You can't strike shrines," said Natalia Korol, a 52-year-old museum worker in Kyiv, speaking to AFP. "It's a shrine. They also say that it's their shrine."

French President Emmanuel Macron condemned the strikes as an attack on "our universal heritage." Kyiv's Metropolitan Epiphanius said: "What more must the Kremlin antichrist do for the world to realise that decisive action must be taken to stop Russian terror against Ukraine and against the very principles of peace?"

EU Commission President Ursula von der Leyen said G7 leaders would discuss "the next steps to increase pressure on Russia, bring Putin to the negotiating table, and end this senseless killing."

The strikes came hours after the US and Iran announced a peace deal, and after Zelensky and Putin both spoke with US President Donald Trump on Sunday about the conflict.

Russia's February 2022 invasion has become Europe's worst conflict since World War II, with thousands of civilians and hundreds of thousands of troops killed. Ukraine has recently stepped up its own drone strikes inside Russian territory.

In the morning Kyiv sun, an AFP reporter saw rescuers carefully cleaning rubble at the monastery as church bells rang out the Ukrainian national anthem.