Nato is warning the war in Ukraine could last for years, as the European Union recommended that Kyiv become a candidate to join the bloc.

Head of Nato Jens Stoltenberg is pushing for the supply of state-of-the-art weaponry to be sent to Ukraine as tensions between Russia and the alliance escalate. Photo: AFP

Russian forces have stepped up the intensity of their assaults. The situation north of Kharkiv, Ukraine's second-largest city, is difficult as Russian forces have been trying to get closer to shell the city again, an official at Ukraine's interior ministry said today.

"Russia is trying to make Kharkiv a frontline city," Vadym Denysenko, an adviser to the interior minister, told Ukraine's national television.

Head of the military alliance, Jens Stoltenberg, said the supply of state-of-the-art weaponry to Ukrainian troops would boost the chance of freeing its eastern region of Donbas from Russian control, Germany's Bild am Sonntag newspaper said.

"We must prepare for the fact that it could take years. We must not let up in supporting Ukraine," Stoltenberg, the secretary-general of the military alliance, was quoted as saying.

"Even if the costs are high, not only for military support, also because of rising energy and food prices."

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British Prime Minister Boris Johnson, who visited Kyiv on Friday, also spoke over the weekend of a need to prepare for a long war.

This meant ensuring "Ukraine receives weapons, equipment, ammunition and training more rapidly than the invader", Johnson wrote in an opinion piece in London's Sunday Times.

"Time is the vital factor," he wrote. "Everything will depend on whether Ukraine can strengthen its ability to defend its soil faster than Russia can renew its capacity to attack."

Speaking to reporters on Saturday, Johnson stressed the need to avoid "Ukraine fatigue". With Russian forces "grinding forward inch by inch", allies must show the Ukrainians they were there to support them for a long time, he said.

Ukraine received a significant boost on Friday when the European Commission recommended it for candidate status, a decision European Union nations are expected to endorse at a summit this week.

That would put Ukraine on course to realise an aspiration seen as out of reach before Russia's February 24 invasion, even if membership could take years.

Intensified attacks

Russian attacks intensified on Ukraine's battlefields.

The industrial city of Sievierodonetsk, a prime target in Moscow's offensive to seize full control of Luhansk - one of the two provinces making up the Donbas - faced heavy artillery and rocket fire again as Russian forces attacked areas around it, the Ukrainian military said.

The military's general staff acknowledged its forces had suffered a setback in the settlement of Metolkine, just southeast of Sievierodonetsk.

"As a result of artillery fire and an assault, the enemy has partial success in the village of Metolkine, trying to gain a foothold," it said in a Facebook post.

Serhiy Gaidai, the Ukrainian-appointed governor of Luhansk, referred in a separate online post to "tough battles" in Metolkine.

Russia's Tass news agency, citing a source working for Russian-backed separatists, said many Ukrainian fighters had surrendered in Metolkine.

To the northwest, several Russian missiles hit a gasworks in Izyum district, and Russian rockets rained down on a suburb of Kharkiv, Ukraine's second-largest city, hitting a municipal building and starting a fire in a block of flats, but causing no casualties, Ukrainian authorities said.

They reported shelling further west in Poltava and Dnipropetrovsk, saying that three Russian missiles destroyed a fuel storage depot in the town of Novomoskovsk, wounding 11 people.

The Ukrainian armed forces general staff said Russian troops on a reconnaissance mission near the town of Krasnopillya had been beaten back with heavy casualties on Saturday.

Reuters could not independently confirm the battlefield accounts.

Zelenskiy: Defenders don't doubt victory

Ukrainian President Volodymyr Zelenskiy said he had visited soldiers on the southern frontline in the Mykolaiv region, about 550km (340 miles) south of Kyiv.

"I talked to our defenders - the military, the police, the National Guard," he said in a video on the Telegram message app on Sunday that appeared to have been recorded on a moving train.

"Their mood is assured: they all do not doubt our victory," Zelenskiy said. "We will not give the south to anyone, and all that is our's we will take back."

Another video showed Zelenskiy in his trademark khaki T-shirt handing out medals and posing for selfies with servicemen.

Zelenskiy's office said he had also visited National Guard positions in the southern region of Odesa to the west of Mykolaiv. The timing of the trips was not revealed.

He has stayed mostly in Kyiv since Russia invaded, although in recent weeks he has made unannounced visits to Kharkiv and two eastern cities near battles.

One of Russian President Vladimir Putin's stated goals when he ordered his troops into Ukraine was to Moscow's southern neighbour outside the West's sphere of influence.

But the war, which has killed thousands, turned cities to rubble and sent millions fleeing, has convinced Finland and Sweden to seek to join Nato. It may have helped Ukraine's bid for EU membership as well.