In two separate decrees Sunday, Zelenskyy dismissed Ukraine’s first female prosecutor general, Iryna Venediktova, who has been leading the country’s efforts to prosecute Russian war crimes, and the chief of the state security agency, known as SBU, Ivan Bakanov, the president’s longtime friend and former business associate.

The dismissals are the highest-profile political firings since Russia invaded Ukraine in late February, and highlight the challenges Ukraine faces to ensure government agencies are not infiltrated by the Russians.

Addressing the dismissals in a latenight video message Sunday, Zelenskyy said more than 60 officials in Bakanov’s and Venediktova’s offices were working against Ukraine in Russian-occupied territory. The cases are among 651 treason and collaboration cases that had been opened against law enforcement officials in Ukraine so far, according to the president.

The number of cases poses “very serious questions to the relevant leadership,” he added.