“Raising the alert level of Russian nuclear forces is a bone-chilling development,” Guterres told reporters Monday. “The prospect of nuclear conflict, once unthinkable, is now back within the realm of possibility.”

Guterres called for a diplomatic solution to the conflict in Ukraine before it the possibility of nuclear war continues to escalate.

“It’s time to stop the horror unleashed on the people of Ukraine and get on the path of diplomacy and peace,” Guterres said. “The appeals for peace must be heard. This tragedy must stop.”