Nearly 10 weeks into a war that has killed thousands of people and flattened Ukrainian cities, Russia was intensifying its assault, Ukraine's defence ministry said, with attacks reported on railway stations used to transport Western arms.
A convoy of buses began evacuating more civilians from the ravaged southeastern port city of Mariupol. Moscow pledged to halt some military operations to allow more evacuations.
Piling pressure on Russia's already battered $US1.8 trillion economy, the EU proposed phasing out imports of Russian crude oil within six months and refined products by the end of this year.
"(President Vladimir) Putin must pay a price, a high price, for his brutal aggression," European Commission chief Ursula von der Leyen said in Strasbourg.
The plan, if agreed by all 27 EU governments, would follow US and British oil bans and be a watershed for the world's largest trading bloc, which remains dependent on Russian energy and must find alternative supplies.
US President Joe Biden said he would speak to other Group of Seven leaders this week about possible further steps against Moscow.
"We're always open to additional sanctions," Biden told reporters in Washington.
Ukraine's Foreign Minister Dmytro Kuleba stressed the urgency of acting to starve Russia's war machine.
"My position is simple: every euro paid to Russia for gas, oil or other goods ends up as rounds of ammunition in Ukraine to kill my compatriots," he told Austrian TV channel Puls 4 in an interview.
The Kremlin said Russia was weighing various responses to the EU plan, adding measures would be costly for European citizens.
A source said EU envoys could reach a deal on Thursday or later this week on the plan, which also targets Russia's top bank, its broadcasters, and hundreds of individuals.
Russian Defence Minister Sergei Shoigu renewed a warning Moscow would seek to hit NATO shipments of weapons into Ukraine.
His ministry said Russian forces disabled six railway stations used to deliver Western arms to Ukraine's east. It later said it hit 77 military targets throughout the day, including ammunition depots and artillery.
Ukrainian authorities said Russian strategic bombers fired 18 rockets "with the aim of damaging our country's transport infrastructure" and confirmed an attack on the railways.
Announcing surprise military drills, Belarus's defence ministry said they posed no threat to neighbours, but Ukraine's border service said it could not rule out Belarusian forces joining Russia's assault.
"We are ready," spokesman Andriy Demchenko said.
Some Russian forces entered Ukraine via Belarus when the invasion began on February 24 but so far no Belarusian troops have been involved in what Moscow calls a "special military operation" to disarm Ukraine and defend its Russian-speaking population from fascists.
The Kremlin on Wednesday dismissed speculation Putin would formally 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 II.
Putin is due to deliver a speech and oversee a military parade in Moscow's Red Square on Monday.
Russia's military said it would pause military activity during the day on May 5, 6 and 7 to allow civilians to evacuate from Mariupol's Azovstal steel works, where civilians and defenders are holding out.
The first evacuees from Azovstal arrived by bus in Zaporizhzhia on Tuesday after sheltering for weeks in bunkers beneath the sprawling Soviet-era complex.
Ukrainian President Volodymyr Zelenskiy urged the UN to help rescue more people from Azovstal.
"The lives of the people who remain there are in danger. Everyone is important to us. We ask for your help in saving them," Zelenskiy said in a statement to UN Secretary General Antonio Guterres.
Russia now claims control of Mariupol, once a city of 400,000 but largely reduced to rubble after weeks of siege and shelling. It is key to Moscow's efforts to cut Ukraine off from the Black Sea and link Russian-controlled territory in the south and east.