WASHINGTON, April 16 (CNN) - Ukrainian President Volodymyr Zelensky told CNN Friday that "all of the countries of the world" should be prepared for the possibility that Russian President Vladimir Putin could use tactical nuclear weapons in his war on Ukraine.

Zelensky told CNN's Jake Tapper in an exclusive interview from the office of the president in Kyiv on Friday that Putin could turn to either nuclear or chemical weapons because he does not value the lives of the people of Ukraine.

"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, switching into English to emphasize his point.

"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."

In the wide-ranging interview, Zelensky spoke about the sinking of a Russian ship, the casualties his military has taken and the emotional toll the war is having on him and his people.

Zelensky has remained in Ukraine throughout the 50-day war with Russia, as Ukraine's forces have resisted the Kremlin's attempts to seize Kyiv and forced Russia to refocus its war efforts on the eastern and southern regions of the country, where Ukraine is anticipating a significant escalation in fighting in the days to come. At the same time, Russia is firing cruise missiles into the outskirts of Kyiv and still maintains the ability to target Ukraine's capital with long-range weaponry.

US officials have warned about the possibility that Putin, if backed into a corner, could turn to the use of tactical nuclear weapons in Ukraine. CIA Director Bill Burns said Thursday that the CIA watches "very intently" over the possibility, while emphasizing that the US has not yet seen any signs that Russia is preparing to take such a step.