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.

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.