President Volodymyr Zelensky has fired the head of Ukraine’s security agency (SBU) and the prosecutor general, citing many cases of treason in the two powerful organisations.
He said more than 60 former employees were now working against Ukraine in Russian-occupied areas.
A total of 651 collaboration and treason cases had been opened against law enforcement officials, he added.
The sacked officials, Ivan Bakanov and Iryna Venediktova, have not commented.
In a video address late on Sunday, Mr Zelensky said: “Such an array of crimes against the foundations of the national security of the state… pose very serious questions to the relevant heads [of the two organisations].”
“Each of these questions will receive a proper answer,” the Ukrainian president added.
The sacking of SBU chief Ivan Bakanov, a childhood friend of Mr Zelensky, follows the high-profile arrest of a former SBU regional head in Crimea, annexed by Russia in 2014. Oleh Kulinych is suspected of treason.
“Everyone who together with him was part of a criminal group that worked in the interests of the Russian Federation will also be held accountable,” Mr Zelensky said. “It is about the transfer of secret information to the enemy and other facts of co-operation with the Russian special services.”
Senor intelligence officials based in Kherson have also been charged and Mr Zelensky suggested that further action would be taken against other SBU officers.
It has long been assumed Ukraine had a problem with Russian infiltration of its security services and in his speech Mr Zelensky sought to lay out the impact of repeated security breaches.
There have been reports for several weeks that Mr Zelensky wanted to replace Mr Bakanov after coming to blame him for failures in stopping the Russian advance in February.
The 47-year-old was picked to head the intelligence agency in 2019 after managing Mr Zelensky’s insurgent campaign for the presidency. Opposition figures criticised the appointment, arguing that the former TV producer was unqualified to lead the SBU.
Ms Venediktova will be succeeded by her deputy, Oleksiy Symonenko, Mr Zelensky said. She took office in 2020 as Ukraine’s first female law enforcement chief after Mr Zelensky fired her predecessor, accusing him of not producing results.
But he warned at the time that someone else would be hired if she could not produce results.
Earlier this month she told the BBC that her office was investigating some 21,000 war crimes and crimes of aggression allegedly committed by Russia since the start of its invasion.