"Now Russia is concentrating its forces. We all know that. It 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 EU chief Ursula von der Leyen.
Zelenskyy called on Europe to implement sanctions more quickly and said the West should take steps to clamp down on sanctions circumvention.
"The terrorist state is increasing the pace of adaptation to sanctions instead. It should be resolved," Zelenskyy said.
Von der Leyen arrived in Kyiv on Thursday with a team of commissioners and the EU's most senior diplomat Josep Borrell ahead of a Ukraine-EU summit on Friday in the war-torn country that is seeking EU membership.
Russian President Vladimir 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 existing sanctions were already "eroding" Russia's economy, "throwing it back by a generation" and estimated that an existing oil price cap alone is 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.
Russian Foreign Minister Sergei Lavrov claimed the EU and specifically von de Leyen had called for Russia to be defeated so its economy would be devastated for decades.
"Is this not racism, not Nazism -- not an attempt to solve 'the Russian question'" Lavrov said, evoking Russia's victory against Nazi Germany in World War II.
Western leaders have dismissed Lavrov's comments as domestic propaganda also meant to sway the developing world, including Africa.
President Vladimir Putin on Thursday vowed a decisive response to any country threatening Russia and lashed out against Germany for promising tanks for Kyiv.
"We have something to respond with," he added. "A modern war with Russia will be completely different."
His spokesman Dmitry Peskov elaborated, saying that as Western deliveries for Ukraine increased to include more powerful weapons, Russia would respond in kind, utiliZing the fullest of its military capacity.
On the front line, Russian forces are pressing Ukrainian troops in the eastern Donetsk region, now the epicenter of fighting.
Moscow has been trying to seize control of Bakhmut in Eastern Ukraine's 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.