Ukraine's head of military intelligence claims a coup effort is already underway to remove Russian President Vladimir Putin.
Maj Gen Kyrylo Budanov told Sky News UK he was "optimistic" about defeating Russia, which would cause the removal of Putin.
"It will eventually lead to the change of leadership of the Russian Federation," Budanov said. "This process has already been launched."
When asked if a "coup" was underway, he told Sky News: "Yes… They are moving in this way, and it is impossible to stop it."
Sky News questioned Budanov about spreading propaganda but he defended the claim saying: "It's my job, it's my work - if not me, who will know this?"
But former deputy assistant secretary-general of NATO's defence investment division, Gordon B Davis Jr, took the opposite view saying he didn't "think we're likely to see a coup in the near future".
"It's tough to talk about the credibility of such a likelihood," he told Sky News in a separate interview.
"I don't put a lot of credence right now into the rumours."
Budanov - who correctly predicted when the Russian invasion would happen when others in his government were publicly sceptical - believes the war in Ukraine will be over by the end of the year.
"Most of the active combat actions will have finished by the end of this year," he said.
"As a result, we will renew Ukrainian power in all our territories that we have lost including Donbas and the Crimea."
Budanov said the hype around the Russian army is a "myth" and it is just a "horde of people with weapons".
"We know everything about our enemy. We know about their plans almost as they're being made," he told Sky.
"Europe sees Russia as a big threat. They are afraid of its aggression.
"We have been fighting Russia for eight years and we can say that this highly publicised Russian power is a myth.
"It is not as powerful as this. It is a horde of people with weapons."
The Ukraine invasion has been ongoing since February 24 with 3573 civilians killed and 3816 injured, the UN confirmed on Friday.
According to the UN, the death toll in Ukraine is likely higher because the armed conflict can delay reports and most of the civilian casualties recorded were caused by the use of explosive weapons with a wide impact area, including shelling from heavy artillery and multiple launch rocket systems, as well as missiles and airstrikes.
On Sunday (NZ time), Ukrainian forces launched a counteroffensive near the Russian-held town of Izium in eastern Ukraine, a regional governor said, in what could prove a serious setback for Moscow's plans to capture the entire Donbas region.