Ukrainian officials have said that 144 of its soldiers, most former defenders of the Azovstal steelworks in the southern port city of Mariupol, had been freed in a prisoner swap with Moscow.

"This is the largest exchange since the start of the full-scale Russian invasion," the main intelligence directorate of Ukraine's defence ministry said on Telegram.

"Of the 144 freed, 95 are Azovstal defenders."

It did not specify when and where the swap took place or how many Russian prisoners were released as part of the exchange.

ut Pro-Russian separatist leader Denis Pushilin said 144 soldiers from Russia and the Donetsk People's Republic - the name of the breakaway region recognised by Moscow -- had "returned home".

The Ukrainian ministry statement said most of their exchanged soldiers had been seriously wounded by bullets or shell fragments, while others were suffering from burns and fractures.

It said that 43 of the freed servicemen belonged to the Azov regiment, a former paramilitary unit that is now integrated into the Ukrainian army.

Russia considers the unit a neo-Nazi organisation and has previously said its soldiers should stand trial.

Ukraine's Prime Minister Denys Shmygal confirmed the exchange on Telegram, saying only that the work to free the prisoners had been "complicated".

Moscow and Kyiv have exchanged prisoners several times since Russia invaded on 24 February.

The most recent previous exchange took place yesterday and involved 17 Ukrainian prisoners.

Russian missiles continue to rain down on Ukraine

Russian forces struck targets in the Mykolaiv region of southern Ukraine today and intensified attacks on fronts across the country as NATO members met in Madrid to plan a course of action against the challenge from Moscow.

Ukrainian President Volodymyr Zelensky told the NATO leaders his country needed more weapons and money to defend itself against Russia, warning that Moscow's ambitions did not stop at Ukraine.

At the summit, President Joe Biden announced additional US land, air and sea deployments across Europe, including a permanent army headquarters in Poland, in response to threats from Russia.

The mayor of Mykolaiv city said a Russian missile strike killed at least three people in a residential building there, while Moscow said its forces had hit what it called a training base for foreign mercenaries in the region.

In the east, the governor of Luhansk province said there was "fighting everywhere" in the battle around the hilltop city of Lysychansk, which Russian troops were trying to encircle.

Ukrainian firemen clearing rubble of a shopping mall targeted by a missile strike in Kremenchuk

The governor of Kryvyi Rih in central Ukraine said Russian shelling had increased there too in the past few days.

"Several villages have been wiped from the face of the earth," Oleksander Vilkul said.

The stepped-up attacks - following a missile strike on a shopping mall killed at least 18 people in central Ukraine on Monday - come as Russian President Vladimir Putin's forces make slow but relentless progress in a war now in its fifth month.

Nonetheless, Western analysts say the Russians are taking heavy casualties and running through resources, while the prospect of more Western weapons reaching Ukraine, including long-range missile systems, made Moscow's need to consolidate any gains more urgent.

Mr Zelensky addressed the NATO summit via videolink

Mykolaiv mayor Oleksandr Senkevych said eight Russian missiles had struck the city, including hitting an apartment block.

Photographs showed smoke billowing from a four-storey building with its upper floor partly destroyed.

Russia's defence ministry said its forces carried out strikes on a military training base for "foreign mercenaries" near the city and also hit ammunition fuel storage. Reuters was not able to independently verify the reports.

A river port and ship-building centre just off the Black Sea, Mykolaiv has been a bastion against Russian efforts to push West towards Ukraine's main port city of Odesa.

Governor Vitaliy Kim said Russian shelling had increased and mostly civilian buildings were being hit.

"It is dangerous in Mykolaiv now, more dangerous than three weeks ago," he said.

Today's Mykolaiv strikes took place just two days after a Russian missile hit the shopping mall in Kremenchuk.

Rescuers there were still searching for dozens of missing on Wednesday.

Pope Francis joined the international condemnation of the Kremenchuk attack, calling it "barbarous".

Moscow has denied targeting the mall and said it had struck an arms depot nearby, which exploded.

Britain's Ministry of Defence said it expected Russia to continue making strikes in an effort to hamper Ukrainian resupplies to the frontlines, and more civilian casualties were likely.

Russia has denied targeting civilian areas but the United Nations says at least 4,700 civilians have been killed since Russia invaded Ukraine on 24 February.

Ukraine believes the true civilian toll is many times higher.

'Fighting everywhere'

Fighting also raged further east in Luhansk province, a key battleground in Russia's assault on the industrial heartland of the Donbas region.

"There is fighting everywhere. The enemy is trying to break through our defences," Luhansk governor Serhiy Gaidai said on television.

The battle for Lysychansk in Luhansk follows the fall of Sievierodonetsk, its sister city across the Siverskyi Donets River on Saturday.

Its capture would expand Russian control of the Donbas, one of Moscow's strategic objectives since its failure to seize Kyiv in the war's early stages.

The Moscow-imposed military-civilian administration in Kherson region said it had begun preparations for a referendum on joining Russia, Russian state news agency TASS reported.

Kherson, a port city on the Black Sea, sits just northwest of the Russian-annexed Crimean peninsula.