KYIV/SLOVYANSK, Ukraine: Russian forces were conducting an all-out assault on Tuesday to encircle Ukrainian troops in twin cities straddling a river in eastern Ukraine, a battle which could determine the success or failure of Moscow’s main campaign in the east.

Exactly three months after President Vladimir Putin ordered Russian forces into Ukraine, 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 was evidence of Ukraine’s biggest military success in recent weeks: pushing Russian forces largely out of artillery range of Kharkiv, as they did from the capital Kyiv in March.

But the decisive battles of the war’s latest phase are still raging further south, where Moscow is attempting to seize the Donbas region of two eastern provinces, Donetsk and Luhansk, and trap Ukrainian forces in a pocket on the main eastern front.

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, with Russian forces 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.

“The intensity of fire on Sievierodonetsk has increased by multiple times, they are simply destroying the city,” he said on TV, adding there were about 15,000 people living there.

Further west in Slovyansk, one of the biggest Donbas cities still in Ukrainian hands, air raid sirens wailed on Tuesday but streets were still busy, with a market full, children riding bikes and a street musician playing violin by a supermarket.

Gaidai said Ukrainian forces had driven the Russians out of the village of Toshkivka just south of Sievierodonetsk. Russian-backed separatists said they had taken control of Svitlodarsk, south of Bakhmut. Neither report could be independently confirmed.

‘Everyone is crazily scared’

Three months into a war that some Western experts predicted Russia would win within days, Moscow still has only limited gains to show for its worst military losses in decades, while much of Ukraine has suffered devastation. Around 6.5 million people have fled abroad, uncounted thousands have been killed and cities have been reduced to rubble.

The war has also had massive international ramifications, including growing food shortages and soaring prices in developing countries that import Ukrainian grain.

European Commission chief Ursula von der Leyen on Tuesday called for talks with Moscow on unlocking wheat exports now trapped in Ukraine because of a Russian blockade in the Black Sea.

Underlining the global geopolitical tensions unleashed by the war, Japan - a key U.S. ally in Asia which has joined Western sanctions against Russia - scrambled jets on Tuesday after Russian and Chinese warplanes neared its airspace during a visit to Tokyo by U.S. President Joe Biden.

In Kharkiv, hundreds of people were still living underground in trains and stations when the authorities asked them to make way on Tuesday so metro service could resume.

In one station, a few people were moving out, while others sat on makeshift beds or stood amid possessions and pets.

“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 below ground for nearly the entire duration of the war.

‘Supid war’

Comments by senior Russian officials on Tuesday suggested plans for a drawn-out conflict ahead. Defence Minister Sergei Shoigu said Russia was deliberately advancing slowly to avoid civilian casualties. Nikolai Patrushev, head of Putin’s security council, said Moscow was not “chasing deadlines” and would fight as long as necessary to eradicate “Nazism” in Ukraine, a justification for the war that the West calls baseless.

The Donbas fighting follows Russia’s biggest victory in months: the surrender last week of Ukraine’s garrison in the port of Mariupol after nearly three months of siege in which Kyiv believes tens of thousands of civilians have 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 rubble 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.

Ukraine’s Foreign Minister Dmytro Kuleba tweeted that the “ruthless” offensive in Donbas showed Ukraine still needed more Western arms, especially multiple launch rocket systems, long-range artillery and armoured vehicles.

Highlighting the obstacles to a diplomatic resolution of the conflict, a new poll on Tuesday showed 82% of Ukrainians believe their country should not sign away any territory as part of a peace deal with Russia under any circumstances.

In Russia, where criticism of the war is banned and independent media has been shut, jailed opposition leader Alexei Navalny used a court appearance by video link from a prison colony to denounce the “stupid war which your Putin started”.

“One madman has got his claws into Ukraine and I do not know what he wants to do with it - this crazy thief,” Navalny said.