Huge explosions from Russian attacks on oil and gas installations lit up the night sky in Ukraine, while Western allies tightened sanctions to banish major Russian banks from the main global payments system.
Ukrainian forces were holding off Russian troops advancing on the capital Kyiv, President Volodymyr Zelenskiy said as the biggest assault on a European state since World War II entered a fourth day.
But the night was brutal, with shelling of civilian infrastructure and targets including ambulances, Mr Zelenskiy said on Sunday.
Casualties from the war are unclear.
A United Nations agency reported 64 civilian deaths and Ukraine claimed to have killed 3500 Russian soldiers.
More than 100,000 refugees, mainly women and children, have poured into neighbouring countries, clogging railways, roads and borders since Russian President Vladimir Putin launched what he called a special military operation on Thursday.
Ignoring weeks of frantic diplomacy and sanctions threats by Western nations seeking to avoid war, Mr Putin has justified the invasion saying “neo-Nazis” rule Ukraine and threaten Russia’s security – a charge Kyiv and Western governments say is baseless propaganda.
Offering a glimmer of hope for talks, the Kremlin sent a diplomatic delegation to neighbouring Belarus.
Ukraine quickly rejected the offer, saying Belarus had been complicit in the invasion.
However, Mr Zelenskiy left the door open for “real negotiations,” elsewhere, an adviser said.
Russian missiles found their mark overnight, including a strike that set an oil terminal ablaze in Vasylkiv, south-west of Kyiv, the town’s mayor said.
Blasts sent huge flames and billowing black smoke into the night sky, online posts showed.
“The enemy wants to destroy everything,” the mayor Natalia Balasinovich said.
Heavy fighting took place for Ukraine’s second city, Kharkiv, in the north-east, where Russian troops blew up a natural gas pipeline, a Ukrainian state agency said.
That blast sent a cloud up into the darkness, though Ukraine’s gas pipeline operator said the transit of Russian gas to Europe via Ukraine was going on as normal.
Kremlin-controlled energy giant Gazprom also said that Russian gas exports via Ukraine to Europe continued normally.
Russian troops later entered Kharkiv, interior ministry adviser Anton Herashchenko said on Telegram.
Videos posted by him and a state agency showed several military vehicles moving on a street and, separately, a burning tank.
Russian-backed separatists in the eastern province of Luhansk said a Ukrainian missile had blown up an oil terminal in the town of Rovenky.
Reuters witnesses in Kyiv reported occasional blasts and gunfire through the night, then three blasts after air raid sirens went off shortly before 9am (1600 AEST).
Ukrainian leaders were defiant.
“We have withstood and are successfully repelling enemy attacks. The fighting goes on,” Mr Zelenskiy said in a video message from the streets of Kyiv posted on his social media.
A US defence official on Saturday said Ukraine’s forces were putting up “viable” resistance to Russia’s air, land and sea advance.
The United States and its allies have authorised more weapons transfers to help Ukraine fight and imposed a range of sanctions on Russia in response to the assault, which threatens to upend Europe’s post-Cold War order.
On Saturday, they moved to block certain Russian banks’ access to the SWIFT international payment system, making it harder for Russia to trade and for its companies to do business.
They also said they would impose restrictions on Russia’s central bank to limit its ability to support the rouble and finance Mr Putin’s war effort.
“We will hold Russia to account and collectively ensure that this war is a strategic failure for Putin,” the leaders of the European Commission, France, Germany, Italy, Britain, Canada and the US wrote.
They did not name the banks that would be expelled. An EU diplomat said some 70 per cent of the Russian banking market would be affected.
Sanctions on Russia’s central bank could limit Mr Putin’s use of his more than $US630 billion ($871 billion) in international reserves, widely seen as insulating Russia from some economic harm.
Google barred Russia’s state-owned media outlet RT and other channels from receiving money for ads on their websites, apps and YouTube videos, similar to a move by Facebook.
Ukraine, a democratic nation of 44 million people, won independence from Moscow in 1991 at the fall of the Soviet Union and has pushed to join NATO and the EU, goals Russia opposes.
Mr Putin has said he must eliminate what he calls a serious threat to his country from its smaller neighbour, accusing it of genocide against Russian speakers in eastern Ukraine – something Kyiv and its Western allies reject as a lie.