Russian President Vladimir Putin has "already started" World War III, and the only way to stop him is to continue using strong economic pressure and military force against him, according to a defiant Ukrainian President Volodymyr Zelenskyy.

"The question is how much territory he will be able to seize and how to stop him," Zelenskyy said in an interview with the BBC this week. "Russia wants to impose on the world a different way of life and change the lives people have chosen for themselves."

"I believe that stopping Putin today and preventing him from occupying Ukraine is a victory for the whole world, because Putin will not stop at Ukraine," he said.

Zelenskyy remains firm in rejecting Putin's demands for a ceasefire that would require Ukraine to withdraw from territory Russia has not captured.

Russia is demanding that Ukraine hand over 20% of the eastern Donetsk region still under Kyiv's control, along with land in the southern regions of Kherson and Zaporizhzhia. Zelenskyy said giving up the territories, even under a ceasefire, is not a solution.

"I don't look at it simply as land," he said. "I see it as abandonment — weakening our positions, abandoning hundreds of thousands of our people who live there. That is how I see it. And I am sure that this 'withdrawal' would divide our society."

Further, Zelenskyy said, Putin would not be satisfied with that concession.

"It would probably satisfy him for a while," he said. "He needs a pause ... but once he recovers, our European partners say it could take three to five years."

"In my opinion, he could recover in no more than a couple of years," he added. "Where would he go next? We do not know, but that he would want to continue [the war] is a fact."

Meanwhile, President Donald Trump said just before the recent ceasefire talks in Geneva that "Ukraine better come to the table fast," as Western diplomats have been saying that Trump agrees with Putin that surrendering the territories is the key to reaching a ceasefire.

Further, analysts are saying that Ukraine will lose the war without making concessions, but Zelenskyy denied that it is the case.

"Will we lose?" he said. "Of course not, because we are fighting for Ukraine's independence."

Zelenskyy also said it is "absolutely clear" that it is "only a matter of time" that Ukraine will recover the territories.

"To do it today would mean losing a huge number of people, millions of people, because the [Russian] army is large, and we understand the cost of such steps," he said. "You would not have enough people, you would be losing them. And what is land without people? Honestly, nothing."

Ukraine also does not have enough weapons, Zelenskyy stressed.

"That depends not just on us, but on our partners," he said. "So as of now, that's not possible, but returning to the just borders of 1991 without a doubt is not only a victory, it's justice."

Zelenskyy also said that the security guarantees he wants from the United States would not only involve Trump but future presidents as well.

"We are all presidents for the appropriate terms," he said, adding that the guarantees must be approved by the U.S. Congress to stand firm.

"We want guarantees for 30 years, for example," said Zelenskyy. "Political elites will change, leaders will change ... they will be voted on in Congress for a reason. It's not just presidents. Congress is needed. Because the presidents change, but institutions stay."

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