KYIV : Huge explosions from Russian attacks on oil and gas installations lit up the night sky in Ukraine early on Sunday, 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 Two entered a fourth day. But the night was brutal, with shelling of civilian infrastructure and targets including ambulances, Zelenskiy said.

Casualties from the war are unclear. A United Nations agency reported 64 civilian deaths and Ukraine claimed to have killed 3,500 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, 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, Zelenskiy rejected talks in Belarus, accusing it of allowing Russian troops through its territory to invade. However, he left the door open for real negotiations elsewhere.

Russian missiles found their mark overnight, including a strike that set an oil terminal ablaze in Vasylkiv, southwest 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," said the mayor, Natalia Balasinovich. Heavy fighting took place for Ukraine's second city, Kharkiv, in the northeast, 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.

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.

Major media team witnesses in Kyiv, reported that the occasional blasts and gunfire through the night, then three blasts after air raid sirens went off shortly before 9 a.m. local time. Ukrainian leaders were defiant. "We have withstood and are successfully repelling enemy attacks. The fighting goes on," Zelenskiy said in a video message from the streets of Kyiv posted on his social media. A U.S. defense official on Saturday said Ukraine's forces were putting up "viable" resistance to Russia's air, land and sea advance.