His threats came after Ukrainian President Volodymyr Zelensky warned that the Kremlin was consolidating its forces for a fresh offensive.
Zelensky was speaking in Kyiv beside EU chief Ursula von der Leyen, who said the bloc was looking to finalise fresh sanctions against Russia by February 24, exactly one year after Putin ordered troops into Ukraine.
In the southern Russian city of Volgograd, Putin said: "It's unbelievable but true. We are again being threatened by German Leopard tanks."
He was speaking at a ceremony commemorating the Red Army's victory against Nazi troops 80 years ago in Stalingrad, as the city was then known.
"We have something to respond with," he added. "A modern war with Russia will be completely different."
Ukraine this month secured promises from the West for deliveries of modern battle tanks to fight Russian forces, and Kyiv is now asking for long-range missiles and fighter jets.
Russia is "preparing to try to take revenge, not only against Ukraine, but against a free Europe and the free world," Zelensky told a joint press conference with von der Leyen.
Putin has insisted that Russia is weathering the barrage of sanctions imposed by Ukraine's Western allies and will continue its military campaign in Ukraine.
"We will introduce with our G7 partners an additional price cap on Russian petroleum products and by the 24th of February -- exactly one year since the war started -- we aim to have the 10th package of sanctions in place," she said.
Von der Leyen arrived in Kyiv on Thursday with the EU's most senior diplomat Josep Borrell ahead of a Ukraine-EU summit on Friday in the war-torn country, which is seeking EU membership.
Zelensky said his country deserved to start accession talks this year to "give energy and motivation to our people to fight."
But EU leaders say the process could take many years.
Russian Foreign Minister Sergei Lavrov claimed the EU and specifically von der Leyen had called for Russia to be defeated so its economy would be devastated.
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