Sign up now for FREE unlimited access to Reuters.com Register KYIV, July 17 (Reuters) – President Volodymyr Zelenskiy on Sunday abruptly fired the head of Ukraine’s powerful internal security service, the SBU, and the prosecutor general, citing dozens of cases of cooperation with Russia by officials from their services. The firings of SBU chief Ivan Bakanov, a childhood friend of Zelensky, and Prosecutor General Irina Venediktova, who played a key role in prosecuting Russian war crimes, were announced by executive orders on the president’s website. The firings are easily the biggest civilian firings since Russia invaded on February 24, forcing the entire Ukrainian state machine to focus on the war effort. Sign up now for FREE unlimited access to Reuters.com Register In a Telegram post, Zelensky said he fired the top officials because it had been revealed that several members of their agencies had cooperated with Russia, a problem he said had affected other agencies. He said 651 cases of alleged treason and collaboration have been opened against prosecutors and law enforcement officials, and that more than 60 officials from Bakanov’s and Venediktova’s agencies are now working against Ukraine in Russian-occupied territories. The sheer number of treason cases reveals the enormous challenge of Russian infiltration that Ukraine faces as it battles Moscow in what it says is a fight for survival. “Such a series of crimes against the foundations of national security of the state… raises very serious questions for the relevant leaders,” Zelensky said. “Every single one of those questions will get the right answer,” he said. Russian troops have seized parts of southern and eastern Ukraine during an invasion that has killed thousands, displaced millions and destroyed cities. It remains unclear how the southern, Russian-held region of Kherson fell so quickly, in contrast to the fierce resistance around Kyiv that forced Russia to eventually withdraw to focus on capturing the industrial heartland of Donbas to the east. In his nightly address to the nation, Zelensky noted the recent arrest on suspicion of treason of the former head of the SBU who oversaw the Crimea region, the peninsula annexed by Russia in 2014 and still regarded by Kyiv and the West as Ukrainian land. Zelensky said he fired the top security official at the beginning of the invasion, a decision he said has now been proven justified. “Sufficient evidence has been gathered to report this person as a suspect of treason. All his criminal activities are documented,” he said. Bakanov was appointed head of the SBU in 2019, one of the new faces to emerge after Zelensky, a former comedian, won the election earlier that year. Zelensky appointed Oleksiy Symonenko as the new prosecutor general in a separate executive order also posted on the president’s website. Sign up now for FREE unlimited access to Reuters.com Register Report by Max Hunder. Additional reporting by Elaine Monaghan. Written by Tom Balmforth. Editing by Gareth Jones and Daniel Wallis Our Standards: The Thomson Reuters Trust Principles.