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Ukraine's President Volodymyr Zelenskyy on Sunday said Russia's leadership was responsible for civilian killings in Bucha, outside Kyiv, where bodies were found lying in the street after the town was retaken by Ukrainian forces.
In a video address, Mr Zelenskyy vowed to investigate and prosecute all Russian "crimes" in Ukraine, saying he had a "special mechanism" to do so.
He spoke as global outrage mounted after the discovery of civilian killings in Bucha, outside Kyiv.
"I want all the leaders of the Russian Federation to see how their orders are being fulfilled," Mr Zelenskyy said, switching from Ukrainian to Russian.
"These kinds of orders. This kind of fulfilment. And there is a common responsibility. For these killings, for this torture, for arms blown off by blasts … for the shots in the back of the head.
"This is how the Russian state will be seen now."
Russia has denied killing civilians in Bucha, which it controlled since the first days of its invasion launched on February 24.
Bodies in the streets were discovered when Ukraine regained control.
Addressing mothers of Russian soldiers, Mr Zelenskyy said: "Why did they do this? Why did they kill them?
"What did the man who was riding a bike do? Why did they torture to death ordinary peaceful people in an ordinary peaceful town?"
"What did the town of Bucha do to your Russia?"
Mr Zelenskyy said he had created a "special mechanism" to investigate Russian "crimes" in Ukraine, pledging to find and punish "everyone" responsible.
He said the mechanism would include "national and international experts, investigators, prosecutors and judges".
Mr Zelenskyy pledged that "everyone guilty of such crimes will be entered in a special Book of Executioners, and will be found and punished".
He ordered Ukraine's Foreign Ministry, prosecutor's office, police and security chiefs to "ensure that the mechanism is operational immediately".
Mr Zelenskyy said Ukrainian authorities were working to "rebuild" Bucha and other towns near the capital that were retaken from Russia.
"All the necessary services are already working in Bucha to bring the town back to life, restore electricity supply, water supply," he said.
"Because Russia was expelled. And Ukraine is returning and brings life back.
Mr Zelenskyy promised to "win this war".