The European Union has proposed its toughest sanctions yet against Russia, including a phased oil embargo, as Ukraine came under further heavy Russian bombardment and nervously monitored large-scale army drills in neighbouring Belarus, a close Moscow ally.
Nearly 10 weeks into a war that has killed thousands of people, uprooted millions and flattened cities and towns in eastern and southern Ukraine, Russia also stepped up attacks on targets in western Ukraine, partly to disrupt Western arms deliveries.
A new convoy of buses began evacuating more civilians from the devastated southeastern port city of Mariupol, which has seen the heaviest fighting of the war so far and where Moscow said remaining Ukrainian forces remained tightly blockaded.
Piling pressure on Russia's already battered $US1.8 trillion ($A2.5 trillion) economy, the European Commission proposed phasing out supplies of Russian crude oil within six months and refined products by the end of 2022. The price of Brent crude jumped three per cent to more than $US108 ($A152) a barrel after the news.
The plan, if agreed by EU governments, would be a watershed for the world's largest trading bloc, which remains dependent on Russian energy and must find alternative supplies. Hungary and Slovakia want to be exempted from the ban for now, sources said.
The EU has yet to target Russian natural gas, used to heat homes and generate electricity across the bloc.
The Kremlin said Russia was looking at various options in response to the EU plans, adding that the sanctions would greatly increase costs for European citizens.
On the war front, Russia's Defence Minister Sergei Shoigu said his military would consider NATO transport carrying weapons in Ukraine, which is not a member of the alliance, as targets to be destroyed, RIA news agency reported. NATO says individual member states are sending military supplies but not troops.
The ministry also said it had hit 40 Ukrainian military targets, including four depots storing ammunition and artillery weapons.
Kyiv and its Western backers say the fascism claim is an absurd pretext for Moscow to wage an unprovoked war of aggression that has driven five million Ukrainians to flee abroad.
The Kremlin on Wednesday dismissed speculation that Putin would declare war on Ukraine and decree a national mobilisation on May 9, when Russia commemorates the Soviet Union's victory over Nazi Germany in World War Two. Putin is due to deliver a speech and oversee a military parade on Moscow's Red Square.
The convoy leaving Mariupol, organised by the United Nations and the International Committee of the Red Cross, was heading for the Ukrainian-controlled city of Zaporizhzhia, Donetsk Governor Pavlo Kyrylenko said. It was not expected to arrive on Wednesday.
He did not say how many buses were in the convoy or whether any more civilians had been evacuated from the vast Azovstal steel works, where the city's last defenders are holding out against Russian forces that have occupied Mariupol.
The first evacuees from Azovstal arrived by bus in Zaporizhzhia on Tuesday after cowering for weeks in bunkers beneath the sprawling Soviet-era steel works.
Ukraine's general staff said the Russian assault on Azovstal was continuing.
Russia now controls Mariupol, once a city of 400,000 but largely reduced to smoking rubble after weeks of siege and shelling. The city is key to Moscow's efforts to cut Ukraine off from the Black Sea - vital for its grain and metals exports - and connect Russian-controlled territory in the south and east.
Moscow has deployed 22 battalion tactical groups near the eastern Ukrainian town of Izium in a possible drive to capture the cities of Kramatorsk and Severodonetsk in Donbas, British intelligence said. Reuters could not immediately verify the report.
The cities are in the eastern Donbas region - Russia's main target along with Ukraine's southern coastline since Moscow failed to take Kyiv, the capital, in the weeks after it invaded.
Ukraine remains defiant despite the unrelenting assault.