Referring to reports of executed civilians, Klitschko told German daily Bild on Sunday that ``what happened in Bucha and other suburbs of Kyiv can only be described as genocide.''

An AP crew on Sunday saw the bodies of at least nine people who appear to have been executed. At least two of them had their hands tied behind their backs. They were all in civilian clothes and at least three were naked from the waist up. One appeared shot in the chest from close range.

Klitschko said Russian President Vladimir Putin was responsible for these ``cruel war crimes,'' adding that civilians had been ``shot with tied hands.''

He called on the the whole world and especially Germany to immediately end gas imports from Russia.

He said that ``especially for Germany, there can only be one consequence: Not a penny should go to Russia anymore, that's bloody money used to slaughter people. The gas and oil embargo must come immediately.''

 Foreign Minister Dmytro Kuleba said Sunday that the killing of civilians in the town of Bucha near the Ukrainian capital was a "deliberate massacre", after the hasty retreat of Russian forces from the area.

"Bucha massacre was deliberate. Russians aim to eliminate as many Ukrainians as they can. We must stop them and kick them out. I demand new devastating G7 sanctions NOW," Kuleba wrote on Twitter.