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.
Shaytanov, who received the rank of major general after a bloody pro-Western uprising in 2014, allegedly passed to his Russian handlers information about secret operations of Ukrainian forces battling against Kremlin-backed separatists in the country's east, the SBU said.
He also planned terror attacks in Ukraine for which he was promised $200,000 and a Russian passport, the SBU claimed.
He is also suspected of planning the murder of Chechen man Adam Osmayev, accused of plotting to kill Russian President Vladimir Putin in 2012.
Osmayev and his wife Amina Okuyeva fought as volunteers alongside the Ukrainian army in the east.
Osmayev survived two attempts on his life but his wife was killed in the second attack when their car was hit by a hail of bullets as it was crossing a railway line in a village near Kiev in 2017.
Ties between Ukraine and Russia were shredded after the annexation of Crimea in 2014.
Moscow went on to support insurgents in eastern Ukraine who launched a bid for independence the same year.
Since then more than 13,000 people have been killed in the conflict.