Watch: Incredible moment Russian politician admits 'it's impossible' to defeat Ukraine on live TV
Appearing on a TV politics programme on the state-owned NTV channel, former state Duma deputy Boris Nadezhdin said Russia's invasion of Ukraine was failing and suggested there should be "peace talks" .
His remarks came after major Russian losses which saw the Ukrainian army take back swathes of lost territory.
"We have to understand it's absolutely impossible to beat Ukraine using those resources and colonial war methods with which Russia is trying to wage war," said Nadezhdin.
"Using contract soldiers, mercenaries, no mobilisation.
"A strong army is opposing the Russian Army, fully supported by the most powerful countries in the economic and technological sense, including European countries.
"I'm suggesting peace talks about stopping the war and moving on to deal with political issues."
Nadezhdin also suggested that Putin had been misled by his advisers, who he claimed had falsely told Putin the Ukrainians would welcome him.
Responding to the video, retired four star US Army general, Barry McCaffrey, described the exchange as remarkable.
"Incredible change of tone on Russian state TV," he said.
"Surprising implicit push back on Putin’s disaster in Ukraine."
Former NATO deputy secretary general, Alexander Vershbow, said: "Amazing this debate is now showing on #Russian State TV... Any chance Putin is watching?"
Ukraine claims to have regained over 3,000 square kilometres (1,158 sq miles) of land in recent days - one of its biggest victories since the war began.
In a defence update early on Monday morning, the British ministry of defence said "rapid Ukrainian successes have significant implications for Russia's overall operational design".
"In the face of Ukrainian advances, Russia has likely ordered the withdrawal of its troops from the entirety of occupied Kharkiv Oblast west of the Oskil River," an intelligence update said.
"Isolated pockets of resistance remain in this sector, but since Wednesday, Ukraine has captured territory at least twice the size of Greater London."
According to Ukrainian president Volodymyr Zelenskyy, Russia subsequently launched retaliatory strikes on "critical infrastructure".
"A total blackout in the Kharkiv and Donetsk regions, a partial one in the Zaporizhzhia, Dnipropetrovsk and Sumy regions," the Ukrainian president tweeted on Sunday night.
"Russian Federation terrorists remain terrorists and attack critical infrastructure.
"No military facilities, the goal is to deprive people of light and heat."
Responding to the Ukrainian advances, former army chief Lord Dannatt said the Russians have “pretty much turned and fled” from the Kharkiv area of Ukraine.
“We are witnessing some incredible scenes,” he told Sky News.
“Although the Ukrainians have made significant advances, there’s a lot of their country still in Russian occupation. So there’s a long way to go."
Ukraine's gains come as Putin weaponises gas supplies from Russia to Europe this winter in retaliation to support from the West for Ukraine.
Last week, Germany's biggest gas company refused to rule out energy rationing after Russia indefinitely halted gas flows via the key Nord Stream 1 pipeline.
Watch: Russia orders troops to withdraw from front line positions after shock Ukrainian advance