The Ukrainian security service (SBU) says it has foiled a Russian plot to assassinate President Volodymyr Zelensky and other high-ranking Ukrainian officials.
Two Ukrainian government protection unit colonels have been arrested.
The SBU said they were part of a network of agents belonging to the Russian state security service (FSB).
They had reportedly been searching for willing "executors" among Mr Zelensky's bodyguards to kidnap and kill him.
Ever since Russian paratroopers attempted to land in Kyiv and assassinate President Zelensky in the early hours and days of the full-scale invasion, plots to assassinate him have been commonplace.
The Ukrainian leader said at the start of the invasion he was Russia's "number one target".
But this alleged plot stands out from the rest. It involves serving colonels, whose job it was to keep officials and institutions safe, allegedly hired as moles.
Other targets included military intelligence head Kyrylo Budanov and SBU chief Vasyl Malyuk, the agency added.
The group had reportedly planned to kill Mr Budanov before Orthodox Easter, which this year fell on 5 May.
According to the SBU, the plotters had aimed to use a mole to get information about his location, which they would then have attacked with rockets and drones.
One of the officers who was later arrested had already bought drones and anti-personnel mines, the SBU said.
SBU head Vasyl Malyuk said the attack was supposed to be "a gift to Putin before the inauguration" - referring to Russia's Vladimir Putin who was sworn in for a fifth term as president at the Kremlin on Tuesday.
The operation turned into a failure of the Russian special services, Mr Malyuk said.
"But we must not forget - the enemy is strong and experienced, he cannot be underestimated," he added.
The two Ukrainian officials are being held on suspicion of treason and of preparing a terrorist act.
The SBU said three FSB employees oversaw the organisation and the attack.
One of them, named as Dmytro Perlin, had been recruiting "moles" since before Russia's full-scale invasion of Ukraine in February 2022.
Another FSB employee, Oleksiy Kornev, reportedly held "conspiratorial" meetings "in neighbouring European states" before the invasion with one of the Ukrainian colonels arrested.
In a released interrogation with one of the suspects, they can be heard describing how they were paid thousands of dollars directly by parcels or indirectly through their relatives. It is not clear whether he was speaking under duress or not.
Investigators insist they monitored the men throughout. We are unlikely to know how close they came to carrying out their alleged plan.
The plot may read like a thriller but it is also a reminder of the risks Ukraine's wartime leader faces.
Last month, a Polish man was arrested and charged with planning to co-operate with Russian intelligence services to aid a possible assassination of Mr Zelensky.
At the weekend Ukraine's president appeared on the Russian interior ministry's wanted list on unspecified charges.
The foreign ministry in Kyiv condemned the move as showing "the desperation of the Russian state machine and propaganda", and pointed out that the International Criminal Court had issued a warrant for Vladimir Putin's arrest.
