Ukrainian President Volodymyr Zelensky warned on Friday that “all countries across the world” should be prepared for Russian President Vladimir Putin to utilise tactical nuclear weapons in his assault on Ukraine.

In an exclusive interview from the president’s office in Kyiv on Friday, Zelensky said that Putin may use nuclear or chemical weapons because he does not respect the lives of Ukrainians.

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“Not only me — all of the world, all of the countries have to be worried because it can be not real information, but it can be truth,” Zelensky said, in a CNN interview.

“Chemical weapons, they should do it, they could do it, for them the life of the people, nothing. That’s why,” Zelensky said. “We should think not be afraid, not be afraid but be ready. But that is not a question for Ukraine, not only for Ukraine but for all the world, I think.”

Zelensky has remained in Ukraine throughout the 50-day war with Russia, as Ukrainian forces have resisted the Kremlin’s attempts to seize Kyiv, forcing Russia to refocus its war efforts on the country’s eastern and southern regions, where Ukraine expects a significant escalation in fighting in the coming days.

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One of Russia’s most important military boats sank in the Black Sea last week, with Ukraine claiming it was the result of a missile strike and Russia claiming it was the consequence of a fire caused by munitions detonation.

At the same time, Russia is launching cruise missiles into the environs of Kyiv and continues to have the capability of targeting Ukraine’s capital with long-range armament.

US officials have warned that if Putin is forced to utilise tactical nuclear weapons in Ukraine, he may resort to using them. CIA Director Bill Burns stated on Thursday that the CIA is “very intently” monitoring the prospect, while noting that the US has seen no indications that Russia is planning to take such a step.

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“Given the potential desperation of President Putin and the Russian leadership, given the setbacks that they’ve faced so far militarily, none of us can take lightly the threat posed by a potential resort to tactical nuclear weapons or low yield nuclear weapons,” he remarked during a public speech at Georgia Tech.