STORY: "I imagine my family in one of those houses, now destroyed and black. I see my granddaughters running away in panic, part of the family eventually killed," Guterres told reporters in Borodianka, surrounded by scorched, windowless apartment blocks.
Guterres said civilians were paying the highest price in the war.
"There is no way the war can be acceptable in the 21st century," said Guterres.
Russia has denied targeting civilians since the Feb. 24 invasion of Ukraine. It has called allegations that Russian forces executed civilians in Bucha while they occupied the town a "monstrous forgery" aimed at denigrating the Russian army.
Guterres is due to hold talks in Kyiv with Ukrainian President Volodymyr Zelenskiy on Thursday.