Ukrainian security authorities said on Tuesday they had uncovered Russian attack plans against President Volodymyr Zelensky and other politicians.
The Ukrainian secret service SBU said that two officers from the Ukrainian state security department responsible for the president's personal protection had been detained in connection with possible attacks.
They are said to have provided the Russian domestic intelligence service FSB with information in return for money and were supposed to have taken part in the attack themselves.
"One of the tasks of the FSB network was to find assassins among the military who were close to the president's personal security so that they could take the head of state hostage and then kill him," the SBU statement in Kiev said. According to the information, the officers held the rank of colonels.
The Ukrainian Prosecutor General's Office confirmed the investigation and the arrests.
However, there was no independent confirmation of the incident outside the Ukrainian security authorities.
SBU chief Vasyl Malyuk and the head of Ukrainian military intelligence, Kyrylo Budanov, were also named as possible targets.
The SBU published what it said were intercepted conversations in which the Russian side offered a Ukrainian officer $50,000 for information and to take part in an assassination attempt.
It is known that Russia sent special commandos to Kiev to capture or kill Zelensky during the start of the full-scale invasion of Ukraine in February 2022. This was not successful.
Since then, the president has been protected by the highest security measures in Kiev and when travelling in Ukraine and abroad.
Zelensky has travelled abroad several times since the war began, calling for additional military equipment to help fend off the Kremlin's forces which are superior in terms of numbers.
Russia is also deploying around 9,000 fighters from Chechnya in its war against Ukraine, according to British estimates.
"It is likely that Chechen special forces bear the brunt of frontline fighting, whilst the bulk of Chechen forces continue to conduct rear area security operations," the British Ministry of Defence said in an update.
Chechen forces have been fighting on Russia's side in Ukraine since 2014, and more units were deployed when the full-scale invasion began in February 2022.
They initially suffered heavy losses there and were then deployed for operations in the hinterland, where they attracted attention, particularly with videos on social media, the ministry said in one of its regular updates based on intelligence findings.
"Since the withdrawal of Russia's private military company Wagner from the frontlines from May 2023, Chechen units have been pressed back into frontline service," the ministry said.
Chechen forces are also training Russian soldiers for the war on Ukraine, the ministry said, citing Chechen data showing around 42,000 soldiers have been trained at the Russian University for Special Forces in the city of Gudermes since February 2022.
"However, it is likely personnel only receive up to 10 days training at the university, bringing the effectiveness of the training and institution into doubt."
As the war rages on in Ukraine, investigations continue abroad into possible war crimes.
The Organization for the Prohibition of Chemical Weapons (OPCW) said on Tuesday that it does not see sufficient evidence of the use of chemical weapons in the war zone in Ukraine, after both Russia and Ukraine accused the other of deploying them.
Both states provided the authority with information on the matter, the OPCW said, adding that the accusations were "insufficiently substantiated."
Nonetheless, the situation in the war zone in Ukraine remains difficult, the OPCW said, adding it was extremely concerned about the possible use of chemical weapons.
Last week, Washington said Russia used chemical substances as a weapon in Ukraine. Moscow denied having done so.
Both Russia and Ukraine are signatories to the Chemical Weapons Convention, so are committed to destroying all their stocks of chemical weapons and not using them.