Britain will end all imports of Russian coal and oil by the end of the year.
Gas imports will be stopped “as soon as possible thereafter”, the Foreign Office said.
Foreign Secretary Liz Truss also announced a full asset freeze on Russia's biggest bank, Sberbank.
It follows Ukrainian President Volodymyr Zelensky's call for the West to punish Vladimir Putin's regime for "war crimes" uncovered in Bucha, where people with their hands tied were found in the streets in apparent executions.
Imports of Russian steel to the UK were also banned, less than a week after the Mirror revealed 3,700 tonnes of Russian “strip mill” had been brought to Britain since the war began on February 24.
Ms Truss said: “We are stepping up our campaign to bring Putin's appalling war to an end with some of our toughest sanctions yet."
"Our latest wave of measures will bring an end to the UK's imports of Russian energy and sanction yet more individuals and businesses, decimating Putin’s war machine.
"Together with our allies, we are showing the Russian elite that they cannot wash their hands of the atrocities committed on Putin's orders. We will not rest until Ukraine prevails."
It came as the US announced that it had sanctioned Russian President Vladimir Putin’s two adult daughters and toughened penalties on Russian banks in retaliation for “war crimes” in Ukraine.
President Joe Biden has also targeted Russian banks and elites among a new package of sanctions.
They include banning any American from investing in Russia and full blocking sanctions on Russia's Sberbank, which holds one-third of Russia's total banking assets, and Alfabank.
The announcement included the Russian President’s adult daughters, Katerina Tikhonovna and Maria Putina, who are both in their 30s and rarely seen in public.
Western officials, meanwhile, have said they fear further Russian atrocities against Ukrainian civilians may be widespread.
The Ukrainian authorities have said that more than 400 bodies of civilians have been discovered in towns round Kyiv which have been captured from the Russians.
One Western official said the comments in the Russian media calling for the “de-nazification” of Ukraine and comparing the country to the Third Reich had created a “toxic information environment”.
“This is a phenomenon which we believe to be widespread,” the official said. “That sort of environment and climate, I’m afraid, absolutely contributes to this sort of thing.
“When you combine that with a force which is failing and failing badly in an operation for which it was perhaps psychologically underprepared, it just a toxic mix.
“The responsibility for this lies with the perpetrators of the acts but it also lies with the Russian leadership. Not only did they order the invasion, they set the tone and the context for this operation as well.”
Keir Starmer has said Labour will support any new sanctions the Government brings forward against Russia over its actions in Ukraine.
“That means military support to help them defend their cities and defend their country,” he said.
“It means being absolutely clear with one voice that these war crimes, and they are war crimes, will end up with those responsible being hunted down.
“If the Government wants tougher sanctions it knows what it needs to do. Put a package before Parliament, we’ll vote for it, it will go through very quickly.”
