Ukraine said Tuesday it had unravelled a Russian plot to assassinate senior Ukrainian political and military figures, including President Volodymyr Zelensky.
Two Ukrainian security officials were arrested for their links to the group, which had aimed to carry out high-profile killings ahead of Russian President Vladimir Putin's inauguration on Tuesday.
"The terrorist attack, which was supposed to be a gift to Putin for his inauguration, was in fact a failure of the Russian secret service," Vasyl Maliuk, head of the Security Service of Ukraine (SBU), said in a statement.
Kyiv says Zelensky has been targeted by Russia on multiple earlier occasions, including at the beginning of the Russian invasion in February 2022.
The SBU said it had exposed a network of agents set up by Russia's Federal Security Service (FSB) tasked with identifying individuals close to Zelensky's security detail who could take the Ukrainian leader hostage and kill him.
"The network, whose activities were supervised by the FSB from Moscow, included two colonels of the State Department of Protection who were leaking classified information to Russia," the SBU said.
Ukraine's State Department of Protection is in charge protecting the president and other senior officials and their families.
A source in Ukrainian law enforcement told AFP that the suspects were detained "a few days ago".
"They were really highly placed men. One of them was a head of department," the source said.
The SBU published photos of masked operatives in camouflage uniform arresting several suspects at night.
In a video posted on the SBU's website, a man with his face blurred said his task was to "test the mood" among the presidential office's security guards, and select someone ready to detain the president, possibly as he went to give his nightly broadcast.
The SBU said Russia also planned to eliminate Maliuk, as well as the head of the Defence Intelligence of Ukraine Kyrylo Budanov and other officials.
Budanov was due to be assassinated before Orthodox Easter, which fell last weekend, the SBU said.
The service's spokesman Artem Dekhtyarenko said the assassin had been promised a reward of up to $80,000.
It published video footage purportedly of an FSB handler telling an agent to surveil a house linked to a target, apparently Budanov, and text when he arrived.
"You'll most likely hear a loud blast," the man says, telling the agent to then use a drone to carry out a secondary strike.
The SBU published what it said were phone messages between a FSB handler and a colonel in the Ukrainian State Department of Protection, who it said personally brought drones, rounds, and anti-personnel mines to Kyiv.
It also gave names of three men it said were FSB handlers working with Ukrainian moles.
Those detained are suspected of treason and preparing a "terrorist act", punishable by life in prison.
Zelensky told The Sun in November that he had survived at least five or six assassination attempts.
Polish and Ukrainian prosecutors announced last month they had detained a man suspected of aiding a Russian plot to assassinate Zelensky.
And the SBU said last August that a woman had been arrested for over a plot to kill the Ukrainian leader by trying to uncover details of his movements outside Kyiv.