Speaking alongside UK Prime Minister Boris Johnson in Kyiv, Zelenskiy said the leaders had discussed steps to contain Russia, adding no one could predict what would happen next in the stand-off.
Zelenskiy said Ukraine was taking a responsible approach to the Minsk ceasefire agreement on ending the war in eastern Ukraine but disagreed with Russia on the sequencing on how the deal would be implemented.
Russian President Vladimir Putin was holding a gun to Ukraine's head in an effort to force a change to the architecture of European security, Johnson said.
"This is a clear and present danger. We see large numbers of troops massing, we see preparations for all kinds of operations that are consistent with an imminent military campaign," Johnson said, adding he would talk to Putin on Wednesday.
"It's about the whole European security architecture, because be in no doubt about what I think President Putin is trying to achieve here. I think that he is trying, by holding a gun as it were to the head of Ukraine, by intimidating Ukraine, to get us to change the way we look at (European security)."
Putin delivered his first public remarks on the Ukraine crisis in weeks on Tuesday and accused the United States and its European allies of having "ignored" Russia's security interests.
Putin said the Kremlin was still reviewing the US and NATO's written responses to Russia's sweeping demands to lower tensions in eastern Europe but it was clear "that the fundamental Russian concerns were ignored".
The Kremlin is insisting on a halt to NATO's eastward expansion and the rolling back of offensive weapons and troops on the eastern flank of the military alliance.
Putin said NATO had imposed security tactics that harmed Russia's interests.Â
"No one's security can be strengthened at the expense of the security of other countries," he said, according to the state-run TASS news agency.
Putin made the comments at a press conference with Hungarian Prime Minister Viktor Orban, the first face-to-face talks between the Russian president and a leader of a NATO member since the escalation of tensions.
Orban said Hungary wanted dialogue between Russia and NATO to continue and that no one in the European Union wanted to see a conflict erupt.
The US has rejected Russia's main demands, such as barring countries like Ukraine from NATO, but has left the door open to renegotiating some post-Cold War security arrangements, with the consent of European allies.
The massing of 100,000 troops along Ukraine's borders, coupled with Russia's demands, have led to a flurry of diplomatic activity in recent weeks, without producing a significant breakthrough.
US Secretary of State Antony Blinken and Russian Foreign Minister Sergei Lavrov spoke by phone on Tuesday but neither side reported any progress.
In a show of support, Johnson and Polish Prime Minister Mateusz Morawiecki were both in Ukraine on Tuesday.
Speaking to Zelenskiy, Johnson said: "We have to face a grim reality, which is that as we stand here, Volodymyr, today, more than 100,000 Russian troops are gathering on your border in perhaps the biggest demonstration of hostility towards the Ukraine in our lifetimes."
"It goes without saying that a further Russian invasion of Ukraine would be a political disaster, a humanitarian disaster, in my view it would also be for Russia, for the world, a military disaster as well," Johnson said.
with reporting from DPA
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