Russian forces sought to encircle Ukrainian troops in twin eastern cities straddling a river as President Volodymyr Zelenskiy warned 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.
Russian forces took control of three towns in the Donetsk region including Svitlodarsk, regional governor Pavlo Kyrylenko told a local 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-night address on Tuesday. "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 the pivotal battlefield there. 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 still 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 move 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, Moscow 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 disrupted 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 supplies 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.
Underlining the global tensions unleashed by the war, Japan - a key U.S. ally in Asia - scrambled jets on Tuesday after Russian and Chinese warplanes neared its airspace during a visit to Tokyo by U.S. President Joe Biden.
Meanwhile, in a move that could push Moscow 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.
Moscow had been allowed to keep paying interest and principal and avert default on its government debt.
Comments by senior Russian officials on Tuesday also suggested plans for a drawn-out conflict ahead.
Nikolai Patrushev, head of Putin's security council, said Moscow 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".
'CRAZILY SCARED'
In Kharkiv, hundreds of people were still 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, the rocket attacks haven't been stopped," said Nataliia Lopanska, who had lived in a metro train for nearly the entire duration of the war.
Russian shelling continued in the city and wider area, regional governor Oleh Sinehubov said.
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 died.
Petro Andryushchenko, an aide to Mariupol's Ukrainian mayor now operating outside the Russian-held city, said the dead were still being found in the rubble.
Around 200 decomposing bodies were buried in debris in a basement of one high-rise building, he said. Locals had refused to collect them and Russian authorities had abandoned the site, leaving a stench across the district.
(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; Editing by Cynthia Osterman)
