President of Ukraine Volodymyr Zelenskyy said Vladimir Putin will use the threat of nuclear war to increase instability in the United States and Europe.

"I think that he's going to continue threatening," Zelenskyy said. "He is waiting for the United States to become less stable. He thinks that's going to happen during the U.S. election. He will be looking for instability in Europe and the United States of America. He will use the risk of using nuclear weapons to fuel that [instability]. He will keep on threatening," he said in an interview with CBS published on Sunday.

"If Ukraine falls, what will happen in ten years? Just think about it. If [the Russians] reach Poland, what's next? A Third World War?" He said.

Zelenskyy admits the counteroffensive is moving slowly but says Ukrainian forces, made up mostly of conscripts, are making progress.

The 700-mile front line has become an artillery duel, with both Russians and Ukrainians firing 40,000 shells a day. The drone war has also slowed progress.

"It's a difficult situation. I will be completely honest with you. We have the initiative. This is a plus," Zelenskyy said. "We stopped the Russian offensive and we moved onto a counter-offensive. And despite that, it's not very fast. It is important that we are moving forward every day and liberating territory." "We need to liberate our territory as much as possible and move forward, even if it's less than [half a mile or] a hundred [yards] we must do it," Zelenskyy continued. "We mustn't give Putin a break."