Ukraine ruled out a ceasefire or any territorial concessions to Moscow as Russia stepped up its attack in the country’s east and south, pounding the Donbas and Mykolaiv regions with air strikes and artillery fire.

Kyiv’s stance has become increasingly uncompromising in recent weeks as Russia experienced military setbacks while Ukrainian officials grew worried they might be pressured to sacrifice land for a peace deal.

“The war must end with the complete restoration of Ukraine’s territorial integrity and sovereignty,” the country’s presidential chief of staff Andriy Yermak said in a Twitter post on Sunday.

Polish President Andrzej Duda offered Warsaw’s backing, telling lawmakers in Kyiv on Sunday that the international community had to demand Russia’s complete withdrawal and that sacrificing any of it would be a “huge blow” to the entire West.

“Worrying voices have appeared, saying that Ukraine should give in to (President Vladimir) Putin’s demands,” Duda said, the first foreign leader to address Ukrainian parliament in person since Russia’s February 24 invasion. “Only Ukraine has the right to decide about its future,” he said.

Speaking to the same parliamentary session, Ukrainian President Volodymyr Zelensky renewed a plea for stronger economic sanctions against Moscow. “Half-measures should not be used when aggression should be stopped,” he said.

Russia is waging a major offensive in Luhansk, one of two provinces in Donbas, after ending weeks of resistance by the last Ukrainian fighters in the strategic southeastern port of Mariupol.

The heaviest fighting focused around the twin cities of Sievierodonetsk and Lysychansk, interior ministry adviser Vadym Denysenko told Ukrainian television on Sunday.

The cities form the eastern part of a Ukrainian-held pocket that Russia has been trying to overrun since mid-April after failing to capture Kyiv and shifting its focus to the east and south of the country.

Russia’s defence ministry said on Sunday its forces pummeled Ukrainian command centres, troops and ammunition depots in Donbas and the Mykolaiv region in the south with air strikes and artillery.

An explosion severely injured a Russian-appointed mayor in the town of Enerhodar, Russia’s RIA news agency reported.

Ukraine’s lead negotiator, Zelensky adviser Mykhailo Podolyak, ruled out any territorial concessions and rejected calls for an immediate ceasefire, saying it meant Russian troops would stay in occupied territories, which Kyiv could not accept.

“The (Russian) forces must leave the country and after that the resumption of the peace process will be possible,” Podolyak said in an interview with Reuters on Saturday, referring to calls for an immediate ceasefire as “very strange”. Concessions would backfire because Russia would use the break in fighting to come back stronger, he said.

Gas snub to Finland

Russian state gas company Gazprom said on Saturday it had halted gas exports to Finland, which has refused Moscow’s demands to pay in roubles for Russian gas after western countries imposed sanctions over the invasion.

Education attack

Russian forces have destroyed 1,873 educational institutions in Ukraine since they invaded in February, President Zelensky said in an overnight address. He described the loss as being on a “colossal scale”.