Russian forces sought to encircle Ukrainian troops in twin eastern cities straddling a river as President Volodymyr Zelenskiy warned that Moscow was seeking to destroy the industrial Donbas region where it has focused its attacks.
Russia is attempting to seize the separatist-claimed Donbas' two provinces, Donetsk and Luhansk, and trap Ukrainian forces in a pocket on the main eastern front.
Musa Magomedov, a Ukrainian member of parliament, said Russian forces were shelling Avdiivka, a town just inside the Ukrainian-controlled part of Donetsk, "in totally inhuman fashion".
"They are killing civilians and destroying the city we built up with such love," Magomedov, the director of a coking plant in Avdiivka, said on Telegram.
Ukraine's military general staff said Russia had intensified the use of aircraft to support ground forces because it lacked supplies of high-precision missiles.
Russian forces took control of three towns in the Donetsk region including Svitlodarsk, regional governor Pavlo Kyrylenko told an affiliate of Radio Free Europe/Radio Liberty.
"The situation in Donbas is extremely difficult. All the remaining strength of the Russian army is now concentrated on this region," Zelenskiy said in a late Tuesday address. "The occupiers want to destroy everything there."
Russia's defence ministry did not immediately respond to an emailed request for comment out-of-hours.
The easternmost part of the Ukrainian-held Donbas pocket, the city of Sievierodonetsk on the east bank of the Siverskiy Donets River and its twin Lysychansk, on the west bank, have become a pivotal battlefield. Russian forces were advancing from three directions to encircle them.
"The enemy has focused its efforts on carrying out an offensive in order to encircle Lysychansk and Sievierodonetsk," said Serhiy Gaidai, governor of Luhansk province, where the two cities are among the last territory held by Ukraine.
Ukraine's military said it had repelled nine Russian attacks on Tuesday in the Donbas where Moscow's troops had killed at least 14 civilians, using aircraft, rocket launchers, artillery, tanks, mortars and missiles.
Reuters could not immediately verify the information.
In a sign of Ukrainian success elsewhere, authorities in its second-largest city, Kharkiv, re-opened the underground metro, where thousands of civilians had sheltered for months under relentless bombardment.
The re-opening came after Ukraine pushed Russian forces largely out of artillery range of the northern city, as they did from the capital, Kyiv, in March.
WORLD WAR THREE?
Three months into the invasion, Russia still has only limited gains to show for its worst military losses in decades, while much of Ukraine has suffered devastation in the biggest attack on a European state since 1945.
More than 6.5 million people have fled abroad, uncounted thousands have been killed and cities have been reduced to rubble.
The war has also caused growing food shortages and soaring prices due to sanctions and disruption of supply chains. Both Ukraine and Russia are major exporters of grain and other commodities.
European Commission chief Ursula von der Leyen accused Russia of using food as a weapon.
Billionaire financier George Soros, also speaking in Davos, said Russia's invasion of Ukraine may have marked the start of World War Three.
"The best and perhaps only way to preserve our civilization is to defeat Putin as soon as possible," he said.
Jailed Russian opposition leader Alexei Navalny on Tuesday lambasted President Vladimir Putin, casting the Kremlin chief as a doomed madman who was butchering the people of both Ukraine and Russia.
"This is a stupid war which your Putin started," Navalny told an appeals court in Moscow via video link from a corrective penal colony. "This war was built on lies."
Underlining the global tensions unleashed by the war, major U.S. ally Japan scrambled jets on Tuesday after Russian and Chinese warplanes neared its airspace as U.S. President Joe Biden visited Tokyo.
Meanwhile, in a decision that could push Russia closer to the brink of default, the Biden administration announced it would not extend a waiver set to expire on Wednesday that enabled Russia to pay U.S. bondholders.
Russia had been allowed to keep paying interest and principal and avert default on its government debt.
Russian lawmakers gave the first stamp of approval to a bill that would allow Russian entities to take over foreign companies that have left the country in opposition to Moscow's actions in Ukraine, a government online portal showed. [nL5N2XG5UG}
On Monday, Starbucks Corp became the latest Western brand to announce it was pulling out of Russia, following a similar decision by McDonald's. The hamburger chain's trademark "Golden Arches" were lowered near Moscow on Monday.
DRAWN OUT CONFLICT
Senior Russian officials suggested in comments on Tuesday the war, which Russia calls a "special operation", may be drawn-out.
Nikolai Patrushev, head of Putin's security council, said Russia would fight as long as necessary to eradicate "Nazism" in Ukraine, a justification for the war that the West calls baseless.
Defence Minister Sergei Shoigu said Russia was deliberately advancing slowly to avoid civilian casualties.
Zelenskiy dismissed such statements as "absolutely unreal".
In Kharkiv, hundreds of people were living underground in trains and stations when the authorities asked them to make way on Tuesday.
"Everyone is crazily scared, because there is still shelling," said Nataliia Lopanska, who had lived in a metro train for most of the war.
The Donbas fighting follows Russia's biggest victory in months: the surrender last week of Ukraine's garrison in the port of Mariupol after a siege in which Kyiv believes tens of thousands of civilians were killed.
Petro Andryushchenko, an aide to Mariupol's Ukrainian mayor now operating outside the city, said the dead were lying in the rubble.
About 200 decomposing bodies were buried in debris in a basement of one high-rise building, he said. Residents had refused to collect them and Russian authorities had abandoned the site.
(Reporting by Oleksandr Kozhukhar in Lviv, Pavel Polityuk and Natalia Zinets in Kyiv, Vitaliy Hnidiy in Kharkiv and Reuters journalists in Mariupol and Slovyansk; Writing by Costas Pitas and Michael Perry; Editing by Cynthia Osterman, Robert Birsel)