The United States and its allies on Wednesday prepared new sanctions on Moscow over civilian killings which President Volodymyr Zelenskiy described as "war crimes."
The US and the EU are set to impose more sanctions on Russia amid allegations of war crimes in the Ukrainian town of Bucha.
Washington is reportedly considering measures targeting Putin's two daughters and Russia's largest bank.
The US also announces it will step up military aid by sending $100m in Javelin anti-tank missile systems to Ukraine.
The assistance comes after Ukraine's President Volodymyr Zelensky listed alleged Russian atrocities, in a speech to the UN Security Council.
Showing a gruesome video, he claimed civilians had been shot in the streets, thrown into wells and crushed by tanks.
Russia denied any war crimes and its UN ambassador repeated debunked claims about bodies in Bucha.
Police and other investigators walked the silent streets of ruined towns around Ukraine’s capital, documenting widespread killings of unarmed civilians and other alleged war crimes by Russian forces that could draw tough new Western sanctions as soon as Wednesday.
While Ukrainian President Volodymyr Zelenskyy kept up demands for war-crimes trials for Russian troops and their leaders, he and others increasingly warn that the Russians are regrouping for a new assault on Ukraine’s east and south.
So far, Ukrainian forces are holding back Russian troops trying to push into the country’s east, but they remain outnumbered in both troops and equipment, Zelenskyy said in a video address to his country late Tuesday.
“But we don’t have a choice — the fate of our land and of our people is being decided,” he said. “We know what we are fighting for. And we will do everything to win.”
Ukrainian prosecutors say they are investigating 4,684 alleged Russian war crimes after the horror of recent atrocities committed in the Ukrainian town of Bucha came to light, prompting global revulsion and a raft of crippling new sanctions against Russia.
According to figures released by the prosecutors office, a total of 4,468 potential war crimes were listed as under investigation as of Tuesday with the figure growing by hundreds every day. An estimated 167 children have also died as a consequence of Russia’s invasion, the agency added.
Ukraine’s prosecutor general Iryna Venediktova described the recently liberated towns surrounding Kyiv as a “tortured region from hell” and vowed to “punish the inhumans who set it up on our land” at a press briefing held from Bucha on Tuesday.
An increasing number of sanctions have been imposed on Russia by the West - moves that are designed to damage the country's economy.
Western countries have frozen the assets of Russia's central bank, to stop it using its $630bn (£470bn) of foreign currency reserves.
Some Russian banks have been removed from the international financial messaging system Swift, which is used to transfer money across borders.
The US has banned all Russian oil and gas imports while the EU and the UK plan to phase out oil imports.
The US, EU and UK have together sanctioned over 1,000 Russian individuals and businesses, including wealthy business leaders considered close to the Kremlin.
The UK, EU and US have also banned the export of dual-use goods- items with both a civilian and military purpose, such as vehicle parts- to Russia.
