MOSCOW, Russia -- President Vladimir Putin on Thursday vowed a decisive response to any country threatening Russia and lashed out against Germany for promising tanks for Kyiv.

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.

Sanctions to 'erode' Russia

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.

But von der Leyen said sanctions were already "eroding" Russia's economy, "throwing it back by a generation". She estimated that an existing oil price cap alone was costing Moscow around 160 million euros every day.

"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 invasion 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.

"Is this not racism, not Nazism," Lavrov said.

Lavrov's comments echoed Putin, who has frequently drawn parallels between what he calls Moscow's "special military operation" in Ukraine and the Soviet war against Nazi Germany.

Putin launched his intervention last year, saying that Russia needed to "de-Nazify" Ukraine.

Von der Leyen's trip comes one day after Kyiv raided the homes of an oligarch and public officials as part of efforts to ease Western concerns about graft.

"I'm comforted to see that your anti-corruption bodies are on alert and effective," von der Leyen said.

'How can I leave?'

On the front line, Russian forces are pressing Ukrainian troops in the eastern Donetsk region, now the epicentre of fighting.

Moscow has been trying to seize control of Bakhmut in the industrial region for months in what has become the longest and bloodiest battle of the invasion.

Residents who remain in the war-scarred town told AFP they will not budge if the Russians arrive.

"How could I leave?" said 75-year-old Natalia Shevchenko.

She said she spends so much time sheltering from bombardments in her basement that she feels "like a mole" as she steps out into the light and her eyes adjust.

"Don't worry," she told AFP as shells whistled in the background. "They're far away. I've now learnt where they're going."

Russian forces have also been shelling the southern region of Kherson, after withdrawing its forces from the region's main city last year.

Separately the United States said Thursday it backs moves to allow athletes from Russia and Belarus to take part in the 2024 Olympics only as neutral athletes prevented from displaying national flags or emblems.

The US position adds to a growing dispute over the status of athletes from Russia and Belarus at the Paris Games.

Ukraine is calling for Russian athletes to be entirely banned over the invasion of Ukraine.