Top allies of Russian President Vladimir Putin have said that Moscow is ready for a prolonged conflict in Ukraine in order to achieve the Kremlin's goals in the pro-Western country.

The hostilities, which entered their fourth month today, have killed thousands of people, displaced more than eight million and forced more than six million refugees to flee across the borders.

"We will continue the special military operation until all the objectives have been achieved, regardless of the massive Western aid to the Kyiv regime and the sanctions against Russia," Defence Minister Sergei Shoigu told regional counterparts from the Russia-led Collective Security Treaty Organisation.

He added that Moscow's efforts to avoid civilian casualties "are of course slowing down the pace of the offensive, but this is deliberate".

Separately, the secretary of Russia's Security Council, Nikolai Patrushev, said that Moscow's offensive would last as long as necessary.

"We are not rushing to meet deadlines," Mr Patrushev told the Russian newspaper Argumenty i Fakty in an interview published today.

"All the goals set by the President of Russia will be fulfilled," he added. "It cannot be otherwise, because the truth, including historical truth, is on our side."

Vladimir Putin said he sent troops to Ukraine to "de-militarise" and "de-nazify" pro-Western Ukraine.

Battles being fought in eastern Ukraine could determine the country's fate, Ukrainian Defence Ministry spokesman Oleksandr Motuzyanyk said today.

Russian forces are trying to encircle Ukrainian troops in twin cities straddling the Siverskyi Donets River in eastern Ukraine. Mr Motuzyanyk said Russian forces had not given up attempts to cross the river.

"Now we are observing the most active phase of the full-scale aggression which Russia unfolded against our country," he told a televised briefing.

"The situation on the (eastern) front is extremely difficult, because the fate of this country is perhaps being decided (there) right now."

Relatives at the funeral of Ukranian soldiers in Synyak, near Kyiv

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.

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Around 200 decomposing bodies were buried 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.

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.

Destroyed Russian tanks on display for public at Mykhailivska Square in Kyiv

"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 today but streets were still busy, with a market full, children riding bikes and a street musician playing violin by a supermarket.

Mr 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.

Hungary imposes state of emergency due to Ukraine war

Meanwhile, Hungary's Prime Minister Viktor Orban has imposed a new state of emergency in the country, citing the challenges posed by the ongoing war in neighbouring Ukraine.

Hungary is already under a state of emergency, linked to the Covid pandemic, which was due to expire next Tuesday.

Exactly three months after Vladimir Putin ordered Russian forces into Ukraine, authorities in its second-largest city Kharkiv reopened 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.

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

People wait on a platform after Kharkiv's underground metro network reopened today

"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.

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 their homes, 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.

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