Russian troops have reportedly entered Ukraine's second city Kharkiv and fighting is under way after Russia said its army has been ordered to launch an offensive “from all directions”.
The head of the regional administration said Russia's light vehicles broke into the city on the fourth day of "special military operations" on Sunday.
"The Ukrainian armed forces are eliminating the enemy," Oleg Sinegubov said, urging residents not to leave shelters.
The Russian defense ministry said its troops had also besieged the southern Ukrainian city of Kherson and the city of Berdyansk in the southeast.
Russian troops had also taken control of Genichesk, a port city along the Sea of Azov, and an airfield near Kherson, ministry spokesman Igor Konashenkov said in a statement.
As of Sunday, the Russian army said it had destroyed 975 military facilities in Ukraine and shot down eight fighter jets, seven helicopters and 11 drones.
Konashenkov said Ukrainian servicemen were laying down arms "en masse". He said that more than 470 Ukrainian servicemen have been detained.
There was no independent verification of any of these claims and Ukraine insists it has inflicted heavy casualties on Russian forces.
Deputy Defense Minister Hanna Malyar claimed that Russian forces have lost about 4,300 servicemen, adding however that the number was being clarified.
She also said on her Facebook page that Russian troops lost about 146 tanks, 27 aircraft and 26 helicopters.
On Saturday, Moscow ordered its troops to advance in Ukraine "from all directions" after saying Ukrainian authorities have refused to hold talks.
Some 400 kilometres to the west of Kharkiv, clashes continued with "sabotage groups" in Kiev but authorities said the capital remained completely under the control of Ukrainian forces.
Since Thursday when Russian President Vladimir Putin announced an offensive, Russian ground forces have pressed into Ukraine from the north, east and south but have reportedly encountered fierce resistance from Ukrainian troops.
“We have withstood and are successfully repelling enemy attacks. The fighting goes on,” Ukraine’s President Volodymyr Zelensky said in a video message purportedly from the streets of Kiev.
On Saturday, the Kremlin said Ukrainian authorities had refused to hold talks, announcing an order for troops to advance in Ukraine "from all directions".
Reports said Russian troops attacked oil and gas facilities in the Ukrainian town of Vasylkiv southwest of Kiev, sparking huge explosions and setting an oil terminal ablaze.
Photographs and videos posted online showed large flames rising into the sky, with the authorities warning residents to be on alert for toxic fumes.
Pro-Russia separatists in Lugansk said an oil terminal was blown up by a Ukrainian missile in the town of Rovenky.
Western governments prepared new sanctions against Moscow, including banishing key Russian banks from SWIFT, the high-security network that connects financial institutions around the world. An EU diplomat said some 70% of the Russian banking market would be affected.
Finland, Sweden, and Denmark said they would close their airspace to Russian planes, joining Bulgaria, the Czech Republic, Estonia, Germany and Poland in ramping up sanctions against Moscow. Russia has also banned planes from those countries from flying over its territory.
An EU official said a European Union-wide ban for Russian flights could be part of a fresh package of sanctions on Moscow to be discussed later on Sunday by the bloc's foreign ministers.
Zelensky hailed the assistance Ukraine was receiving from its allies.
"This is already real. We are receiving weapons, medicine, food, diesel, and money," Zelensky said in a video address. "A powerful coalition in support of Ukraine has been formed -- an anti-war coalition."
Zelensky also urged the United Nations and its Western allies to scrap Russia's voting power at the Security Council and claimed that Russian actions verged on "genocide".
Similarly, Russian President Vladimir Putin congratulated members of special forces on their professional holiday, saying they fought "heroically" in Ukraine.
Kremlin spokesman Dmitry Peskov sad Russia is ready for talks with Ukraine, adding that a delegation from Moscow has already arrived in the Belarusian city of Gomel.
"We will be ready to begin these talks in Gomel," Peskov said.
Ukrainian authorities have refused to hold talks in Belarus which has allowed Russian troops passage to Ukraine.
An adviser to Zelenskiy was quoted as saying that Moscow's decision to send a delegation to Belarus for talks was "propaganda", adding Ukraine wanted only "real" negotiations with Russia over its military offensive, without ultimatums.
British Foreign Minister Liz Truss waded into the standoff, saying there could be no talks with Russia over Ukraine while Moscow has troops in its neighbor.
European Union foreign policy chief Josep Borrell said he will propose using EU funds to help finance weapons and other supplies such as fuel for Ukraine.
"These aim to finance the supply of lethal material to the heroic Ukrainian army, which is fighting with fierce resistance against the Russian invaders and provide urgently needed non-lethal supplies, such as fuel," he said ahead of a virtual meeting to discuss fresh sanctions on Russia.
Greece said it was sending military supplies to Ukraine in response to a request from the Ukrainian government. The Czech government also said it will approve further military material help for Ukraine.
The United Nations Refugee Agency said more than 120,000 Ukrainians have left the country since Russia started the military campaign on Thursday.
Macron predicts long war
French President Emmanuel Macron said the world must brace for a long war between Russia and Ukraine, warning that the conflict would have “lasting consequences”.
Macron’s presidential office also said in a statement that France would send more military equipment, as well as fuel, to Ukraine to help fight off the Russian offensive and slap more economic sanctions on Moscow.
The statement said the new sanctions would encompass “national measures to freeze the financial assets of Russian figures” as well as “new measures” to be taken “with European partners concerning the SWIFT” interbank system.
EU Council President Charles Michel also said on Twitter that the European Union would facilitate the delivery of military aid to Ukraine.
EU defence in action in support to #Ukraine
— Charles Michel (@eucopresident) February 26, 2022
Will facilitate deliveries of military aid from #EU to Ukraine.
Democratic #Ukraine will prevail. @ZelenskyyUa https://t.co/JQomw768DD