Polish Prime Minister Donald Tusk on Monday called the conflict in Ukraine a battle between "good and evil," and vowed more support for Ukraine on his first visit to the war-torn country since returning to power.
The surprise trip came as the Kremlin blamed Ukraine for a weekend attack on a Baltic gas terminal, the latest in a series of apparent Ukrainian air strikes on Russian energy infrastructure.
Tusk is among a flurry of European leaders to have visited Kyiv in recent weeks to reassure Ukraine of international support as its biggest political and military backers struggle to secure aid.
"I am not ashamed to use these big words: it is here, in Ukraine, that the world front between good and evil runs," Tusk told a press conference alongside Ukrainian President Volodymyr Zelensky.
Tusk said Poland stood ready to deepen its financial and military cooperation with Ukraine and promised that Warsaw would do "everything" in its power to help its neighbour.
"The security of the Polish nation and the Polish state is also at stake in this fight," he said.
Zelensky told Tusk that "unity" between Kyiv and Warsaw -- as well as among European countries -- was "a strong shield" against Russian efforts to divide Ukraine's Western allies.
"This unity -- this unity of the whole of Europe -- cannot be lost," he told Tusk, moments after air raid sirens had rung out over the Ukrainian capital.
Zelensky also lashed out at "sceptical" members of the NATO alliance holding out against Ukrainian membership of the bloc, and said his country is "fighting this scepticism".
Tusk's visit also aimed to address tensions between the neighbours, including protracted border blockades by Polish hauliers.
Polish truckers blocked the Ukraine border from November until last week, demanding the return of restrictions to enter the EU for Ukrainian competitors.
The EU had waived the permits system after Russia invaded in February 2022, but Polish truckers want it reintroduced, saying their earnings have been hit.
Just hours before Warsaw announced the visit, Kyiv said it had repelled a Russian assault with eight Iranian-designed attack drones.
Kyiv has made gaining control of the airspace a priority for this year and urged the West to supply more air defence systems.
Ukraine's air force said Russian forces launched the drones from the southern Primorsko-Akhtarsk region. It added that they had been downed by defence systems in southern and central regions of Ukraine.
There were no immediate reports of damage from falling debris.
There have been several aerial assaults on border regions of Russia that have targeted oil storage facilities.
Ukrainian security sector sources have claimed responsibility for some of the attacks, but Kyiv and the Ukrainian military have remained tight-lipped on attacks inside Russia.
Kremlin spokesman Dmitry Peskov however blamed Kyiv for a blaze over the weekend at the port of Ust-Luga near Saint Petersburg.
"The Kyiv regime continues to show its bestial face. They are striking civil infrastructure, people," Peskov told reporters when asked about the blaze at a natural gas terminal.
Operator Novatek had said the fire was caused by an "external factor," without elaborating.
Even though the sprawling front line cutting through eastern and southern Ukraine has barely shifted in the last year, Russian forces have continued to pound towns and villages near the fighting.
AFP journalists on Monday saw the body of one person killed in a strike on the eastern Ukrainian town of Kramatorsk at around 0730 GMT.
The strike rocked an industrial area on the eastern outskirts of the town in the Donetsk region, which the Kremlin says is part of Russia.
AFP reporters saw debris strewn on the street beneath an administrative building with a destroyed roof and windows blown out by the strike.
The body of a man lay at the wheel of his car -- its front left door open -- on a street next to the damaged building.
Police ushered bystanders away, warning of a potential follow-up attack.
The regional governor said the victim was a 49-year-old man and that his 31-year-old daughter was also wounded.
Separately, the governor of the southern region of Kherson said a resident was killed by a Russian drone strike. The Kremlin says it has annexed the region.
