Kyiv's mayor Vitali Klitschko has demanded Western countries cut all business and energy ties with the Kremlin to halt the flow of "blood money".
It comes amid a warning that atrocities worse than that allegedly committed by Russia in Bucha may have been carried out in neighbouring Ukrainian towns.
Volodymyr Zelensky, Ukraine’s president, said that areas in the north of the country, which have only recently been liberated from invading Russian forces, are yet to be discovered but could have suffered even worse than Bucha.
"There is already information that the number of victims may be even higher in Borodyanka and some other liberated cities," he said.
With Russian forces having been pushed back from areas surrounding Kyiv amid fierce battles in recent days, Ukrainian forces are only now discovering the grim reality of the last six weeks of fighting.
Russia has denied that its forces carried out any atrocities and claimed to have "empirical evidence" proving its forces were not involved.
At the weekend, images emerged from Bucha showing several bodies apparently shot at close range, along with makeshift burials and a mass grave.
Satellite images taken in March by US company Maxar Technologies showed bodies of civilians on a street in Bucha, which was occupied by Russian forces until about 30 March, undercutting Kremlin claims that the scenes were staged.
The discovery in Bucha has increased pressure on the West to take an even tougher line against Russia.
Mr Klitschko on Tuesday called on Western officials to once-and-for-all sever links with Russia.
"Every euro, every cent that you receive from Russia or that you send to Russia has blood, it is blood money and the blood of this money is Ukrainian blood, the blood of Ukrainian people," Mr Klitschko said.
Europe still gets about a third of its natural gas needs from Russia.
The response to the atrocities in Bucha from European countries, including Germany, France and Italy, has so far extended to expulsions of Russian diplomats. Moscow said it would respond in kind.
Further sanctions are also being proposed, with the European Union's executive pushing for a ban on coal imports from Russia. A ban on European exports of goods including semiconductors and computers would also be applied, and Russian ships would be stopped from entering EU ports.
Mr Zelensky visited Bucha on Monday, where he said the alleged actions of Russians in the town could affect ongoing peace talks. It is “very hard to talk, when you see what they have done here”, he said.
Speaking later in an interview with Ukrainian journalists broadcast on national television, he said: "All of us, including myself, will perceive even the possibility of negotiations as a challenge.
"The challenge is internal, first of all, one's own, human challenge. Then, when you pull yourself together, and you have to do it, I think that we have no other choice."
He said the events in Bucha were unforgivable but Ukraine and Russia should take the difficult option of pursuing talks, and signalled that Moscow should recognise what its troops were alleged to have done.
Russia has said it is open to the possibility of a meeting between presidents Putin and Zelensky, but it can only happen once a document has been agreed.
Additional reporting by agencies
