Russia accused Ukraine on Wednesday of a failed attempt to assassinate President Vladimir Putin in a drone attack on the Kremlin citadel in Moscow, and threatened to retaliate.

Kyiv denied any role in the reported incident, with a senior aide to President Volodymyr Zelenskiy calling it a sign the Kremlin was planning a major new attack on Ukraine.

Shortly after the Kremlin announcement, Ukraine reported alerts for air strikes over Kyiv and other cities.

“Two unmanned aerial vehicles were aimed at the Kremlin. As a result of timely actions taken by the military and special services with the use of radar warfare systems, the devices were put out of action,” the Kremlin said in a statement.

“We regard these actions as a planned terrorist act and an attempt on the president’s life, carried out on the eve of Victory Day, the May 9 Parade, at which the presence of foreign guests is also planned,” it said. It said fragments of drones were scattered in the Kremlin grounds but there were no injuries or damage.

Putin himself was safe.

Putin has established identical offices in multiple locations, all furnished and decorated the same in every detail, with matching desks and wall hangings, according to Gleb Karakulov, a captain in the Federal Protection Service responsible for guarding the President who defected and recently gave interviews about his experiences. In live broadcasts, it would be impossible to discern where he was.

“The Russian side reserves the right to take retaliatory measures where and when it sees fit.”

A video posted by Baza, a Telegram channel with links to Russia’s law enforcement agencies, showed a flying object approaching the dome of a Kremlin building overlooking Red Square, exploding in a burst of light just before reaching it. Another video posted on a neighbourhood Internet group showed a plume of smoke over the Kremlin’s gold domes. Reuters could not independently verify the videos.

In comments sent to Reuters, Ukrainian presidential advisor Mykhailo Podolyak said: “Of course, Ukraine has nothing to do with drone attacks on the Kremlin. We do not attack the Kremlin because, first of all, it does not resolve any military tasks.”

Podolyak said the accusation, along with a separate announcement that Russia had caught suspected saboteurs in Crimea, “clearly indicates the preparation of a large-scale terrorist provocation by Russia in the coming days”.

Ukraine’s president, Volodymyr Zelensky, is in Finland on Wednesday on a rare trip outside the country. In a joint news conference with Finland’s President, Sauli Niinisto, Zelensky thanked Finland for its continuous support of “our freedom and territorial integrity and sovereignty”. The alleged attack on the Kremlin did not come up at the news conference.

A strike on the Kremlin would be an audacious attack in the heart of Moscow. Russia’s claim came as Ukraine prepares to launch a counteroffensive aimed at retaking territory seized by Moscow’s troops.

‘Large shaker of salt’

The US secretary of state, Antony J. Blinken, was asked at a public event at The Washington Post about the Kremlin reports of a drone attack. He answered: “I’ve seen the reports. I can’t in any way validate them. We simply don’t know.” He added: “I would take anything coming out of the Kremlin with a very large shaker of salt.”

When asked about the US position on any possible attacks by Ukraine on Russia, he said, “These are decisions for Ukraine to make about how it’s going to defend itself.”