Ukrainian President Volodymyr Zelensky said on Friday that Ukrainian officials believe 2,500 to 3,000 Ukrainian troops have died in the war, compared with 19,000 to 20,000 Russian deaths.

Zelensky told CNN’s Jake Tapper in an interview that roughly 10,000 Ukrainian troops have been injured, adding that it’s “hard to say how many will survive.”

As for civilian deaths throughout the 50-day war in Ukraine, Zelensky said the number is harder to evaluate.

“It is very difficult to talk about civilians, since south of our country, where the towns and cities are blocked — Kherson, Berdyansk, Mariupol further east and the area to the east where Volnovakha is — we just don’t know how many people have died in that area that is blocked,” Zelensky said.

Zelensky also warned that Putin’s disregard for Ukrainian lives means the world should be prepared for the Russian president to use nuclear or chemical weapons.

“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.”

CIA Director Bill Burns echoed that sentiment this week, saying during public remarks that considering Putin’s military setbacks, “none of us can take lightly the threat posed by a potential resort to tactical nuclear weapons or low-yield nuclear weapons.”