Speaking from the heavily-guarded government enclave in Kyiv, Zelensky insisted Ukraine would not surrender territory in exchange for a ceasefire, warning that any pause in fighting would only give Russia time to regroup.
"I believe that Putin has already started it [World War Three ed.]," he said.
"The question is how much territory he will be able to seize and how to stop him."
Rejecting Moscow's demands that Ukraine withdraw from parts of eastern and southern Ukraine, Zelensky said he saw such concessions not as a compromise but as "abandonment".
"I don't look at it simply as land. I see it as abandoning hundreds of thousands of our people who live there."
He also warned that a ceasefire would not bring lasting peace.
Putin, he said, could recover militarily within "a couple of years" and would then look to expand further.
On the question of US security guarantees, Zelensky stressed they needed to be approved by Congress.
"The presidents change, but institutions stay," he said.
He ended the interview in English, striking a note of cautious optimism.
"One of these parallel ways will, I think, bring success. God bless, we will be successful."
Russia launched its full-scale invasion of Ukraine on 24 February 2022, triggering Europe's largest armed conflict since the Second World War and prompting sweeping Western sanctions against Moscow.
(ał)
Source: BBC News