In a bellicose speech on Monday at a youth festival in the southern city of Sochi, Medvedev said Russia would prosecute what it calls its "special military operation" until the other side capitulated.
The former president and prime minister said what he called historical parts of Russia should "return home".
Medvedev spoke in front of a map of Ukraine, which showed the country as a much smaller landlocked slice of territory squeezed up against Poland with Russia in complete control of its east, south and Black Sea coast.
Comment: Medvedev has shown this map before, such as back in 2022, and one could suppose that the intended message is: should Ukraine continue as it is, that is what will be left of it.
"One of Ukraine's former leaders said at some point that Ukraine is not Russia," Medvedev said.
"That concept needs to disappear forever. Ukraine is definitely Russia," he said to applause from the audience.
Medvedev said peace talks would not be possible with the current Ukrainian leadership, led by President Volodymyr Zelenskyy.
Comment: Footage:
He said any future Ukrainian government that wants talks would need to recognise what he called the new reality on the ground.
Commenting on East-West relations, Medvedev, who accused US special forces and military advisers of waging war against Russia, said ties between Moscow and Washington were worse than during the 1962 Cuban missile crisis.
On Sunday, Medvedev joined a chorus of Kremlin voices accusing Western countries of participating in the war in Ukraine after a wiretap recording of German military officials was published on Russian social media.
The discussion revolved around the potential impact of Ukraine's use of German-made Taurus missiles.
The conversation included remarks about aiming the missiles at targets such as the Kerch Bridge, which links the Russian mainland to occupied Crimea, which was annexed by Russia in 2014.
German Chancellor Olaf Scholz has so far refused to send the missiles to Ukraine, fearing it would escalate the conflict.
In a Telegram post on Sunday, Medvedev criticised the German military and claimed the country was preparing to attack Russia.
Comment: Indeed, Medvedev is not only correct about ties, but the West's intention to attack Russia, as well as its direct participation in the war, is now irrefutable: