The Ukrainian security service said on Tuesday it has detained a high-ranking employee on suspicion of spying for Russia and planning terror attacks.

The investigation has uncovered "indisputable evidence" including audio and video recordings which show that Major General Valery Shaytanov had planned terror attacks in Ukraine and collected intelligence for Russia's FSB security service, the SBU service said.

"Unfortunately, a man who had to protect Ukraine in fact worked against it," SBU chief Ivan Bakanov was quoted as saying in a statement.

Shaytanov was detained as a result of "a complicated, long-term, multi-level special operation," Bakanov said.

Authorities are gearing up to lay charges of state treason and planning terror attacks against the detained man, the security service added.