Russia must withdraw completely from Ukraine as part of any ceasefire deal, Kyiv and its closest allies said on Sunday, as they faced a determined push from Moscow in the country’s east after three months of war.
Losing even an inch of Ukrainian territory would be a huge blow to the international community that has rallied behind Kyiv, Poland’s President Andrzej Duda said on Sunday.
He became the first foreign leader to address MPs in person in Kyiv since the start of the invasion.
"Worrying voices have appeared, saying that Ukraine should give in to Putin's demands," President Duda said.
"Only Ukraine has the right to decide about its future."
Ukraine's lead negotiator on Saturday ruled out any ceasefire that would involve Russian forces remaining in occupied areas or any deal that involved ceding territory.
Mr Zelenskyy’s adviser, Mykhailo Podolyak, said that any concessions would allow Russia to regroup and come back hard after any break in fighting.
"The war will not stop. It will just be put on pause for some time," Mr Podolyak told Reuters. "They'll start a new offensive, even more bloody and large-scale."
Moscow, meanwhile, showed no sign of letting up a major offensive in the eastern Donbas region after ending weeks of resistance by Ukrainian fighters holed up in the strategically important city of Mariupol.
The battlefield victory gives Russia command of a land route linking the Crimean Peninsula, which Moscow seized in 2014, with mainland Russia and parts of eastern Ukraine held by pro-Russia separatists.
Russian forces continued to bombard frontline Ukrainian cities seeking to gain military momentum after failing to secure most of its key goals in the first weeks of the war. It has shifted its focus from trying to capture Kyiv and shifting its focus to the south and east of the country.
The Russian defence ministry said on Sunday its forces pounded Ukrainian command centres, troops and ammunition depots in Donbas and the Mykolayiv region in the south with air strikes and artillery.
Western officials have warned that no major breakthrough this summer could lead to a long-term stalemate.
Russia would be unable to make any significant breakthroughs, while Ukrainian forces — bolstered by western arms — are still too small to force Russia out of the country.
Despite ruling out any concessions, Ukraine has already accepted that talks with Russia are inevitable to end the war.
"There are things that can only be reached at the negotiating table," President Volodymyr Zelenskyy told Ukrainians on Saturday.
The war, he said, "will be bloody, there will be fighting, but it will only definitively end through diplomacy".
Russian-backed separatists already control parts of Luhansk, one of two provinces in Donbas, and the neighbouring Donetsk province before the invasion, but Moscow wants to seize the remaining Ukrainian-held territory in the region.
Ukraine's general staff reported continued heavy Russian shelling of twin cities Sievierodonetsk and Lysychansk in the Luhansk region.
Russian state gas company Gazprom responded to Western sanctions on Saturday by halting gas exports to Finland, which has refused Moscow's demands to pay in roubles for Russian gas.
Finland said it was prepared for the cut-off of Russian flows. It applied together with its Nordic neighbour Sweden on Wednesday to join the Nato military alliance, although that is facing resistance from NATO member Turkey.
Western nations have also stepped up weapons supplies to Ukraine. On Saturday, Kyiv received another huge boost when US President Joe Biden signed a bill to provide nearly $40 billion in military, economic and humanitarian aid.
Russian President Vladimir Putin calls the invasion a "special military operation" to disarm Ukraine and rid it of radical anti-Russian nationalists.
Ukraine and its allies have dismissed that as a baseless pretext for the war, which has killed thousands of people in Ukraine, displaced millions and shattered cities.
Ukraine will keep up its diplomatic battle with Mr Zelenskyy speaking by video to the annual gathering of the world’s elite at Davos, Switzerland.
The country’s foreign minister, Dmytro Kuleba, will also head a significant delegation at the event.
The Russian invasion means that its business and political leaders have not been invited this year.