Russia pressed its offensive in Ukraine’s eastern Donbas region Sunday as Poland’s president traveled to Kyiv to support the country’s Western aspirations, becoming the first foreign leader to address the Ukrainian parliament since the start of the war.

Ukrainian lawmakers stood to applaud Polish President Andrzej Duda, who thanked them for the honor of speaking where “the heart of a free, independent and democratic Ukraine beats.” Duda received more applause when he said that to end the conflict, Ukraine did not need to submit to conditions given by Russian President Vladimir Putin.

“Unfortunately, in Europe there have also been disturbing voices in recent times demanding that Ukraine yield to Putin’s demands,” he said. “I want to say clearly: Only Ukraine has the right to decide about its future. Only Ukraine has the right to decide for itself.”

Duda’s visit, his second to Ukraine’s capital since April, came as Russian and Ukrainian forces engaged in battles scattered along a 551-kilometer (342-mile) wedge of the country’s eastern industrial heartland, and as Ukraine pursues European Union membership.

After declaring full control this week of a sprawling seaside steel plant that was the last defense holdout in the port city of Mariupol, the Russian military launched artillery and missile attacks in the Donbas, seeking to expand the territory Moscow-backed separatists have held since 2014.

To bolster its defense against the invasion, Ukraine’s parliament voted Sunday to extend martial law and the mobilization of armed forces for a third time, until Aug. 23.

Ukrainian President Volodymyr Zelenskyy has stressed that the 27-member EU should expedite Ukraine’s request to join the bloc as soon as possible due to Russia’s invasion. Ukraine’s potential candidacy is set to be discussed at a Brussels summit in late June.

Poland’s government is ramping up efforts to persuade other EU members that are more hesitant about accepting the war-ravaged country as a member. Zelenskyy said Duda’s visit represented a “historic union” between Ukraine, which declared independence from the Soviet Union in 1991 and Poland, which ended communist rule two years earlier.

“This is really a historic opportunity not to lose such strong relations, built through blood, through Russian aggression,” Zelenskyy said. “All this not to lose our state, not to lose our people.”

Poland has welcomed millions of Ukrainian refugees and become a gateway for Western humanitarian aid and weapons going into Ukraine. It is also a transit point into Ukraine for some foreign fighters, including from Belarus, who have volunteered to fight against the Russian forces.

“Despite the great destruction, despite the terrible crime and great suffering that the Ukrainian people suffered every day, the Russian invaders did not break you. They failed at it. And I believe deeply that they will never succeed,” he told the Verkhovna Rada, Ukraine’s legislature.

Duda also credited “the United States and the leadership of President Joe Biden” for the unity Western nations have shown in supporting Ukraine and imposing sanctions against Russia.

“Kyiv is the place from which one clearly sees that we need more America in Europe, both in the military and in this economic dimension,” said Duda, a right-wing populist leader who clearly preferred former President Donald Trump over Biden during the 2020 election.

On the battlefield, Russia appeared to have made slow grinding moves forward in the Donbas in recent days. It intensified efforts to capture Sievierodonetsk, the main city under Ukrainian control in Luhansk province, which together with Donetsk province makes up the Donbas.

Luhansk Gov. Serhii Haidai said the sole functioning hospital in the city has just three doctors and enough supplies for 10 days.

In a general staff morning report, Russia also said that it was preparing to resume its offensive toward Slovyansk, a city in Donetsk province that is critical to Russia’s objective of capturing all of eastern Ukraine and saw fierce fighting last month after Moscow’s troops backed off from Kyiv.

In Enerhodar, a Russian-held city 281 kilometers (174 miles) northwest of Mariupol, an explosion injured the Moscow-appointed mayor at his residence Sunday, Ukrainian and Russian news agencies reported.

Ukraine’s Unian news agency said a bomb planted by “local partisans” exploded, injuring 48-year-old Andrei Shevchuk. Many of Enerhodar’s residents work at the Zaporizhzhia Nuclear Power Plant, which is Europe’s largest nuclear plant.

With Russia claiming to have taken prisoner nearly 2,500 Ukrainian fighters from the besieged Mariupol steel plant, concerns grew about their fate and the future facing the remaining residents of the city, now in ruins with more than 20,000 residents feared dead.

Family members of the fighters, who came from a variety of military and law enforcement units, have pleaded for them to be given rights as prisoners of war and eventually returned to Ukraine. Deputy Prime Minister Iryna Vereshchuk said Saturday that Ukraine “will fight for the return” of every one of them.

The Azovstal steel plant for weeks was the last defense holdout in Mariupol and became a symbol of Ukrainian tenacity. Its seizure gave Russian President Vladimir Putin a badly wanted victory in the war he began nearly three months ago.

Denis Pushilin, the pro-Kremlin head of the self-proclaimed Donetsk People’s Republic, vowed the Ukrainian fighters from the plant would face tribunals. He said the fighters included some foreign nationals, though he did not provide details.

The Ukrainian government has not commented on Russia’s claim of capturing Azovstal. Ukraine’s military had told the fighters their mission was complete and they could come out. It described their extraction as an evacuation, not a mass surrender.

Mariupol Mayor Vadim Boychenko warned Saturday that the city faced a health and sanitation “catastrophe” from mass burials in shallow pits across the ruined city as well as the breakdown of sewage systems. An estimated 100,000 of the 450,000 people who resided in Mariupol before the war remain.

With Russia controlling the city, Ukrainian authorities are likely to face delays in documenting evidence of alleged Russian atrocities in Mariupol, including the bombings of a maternity hospital and a theater where hundreds of civilians had taken cover.

Meanwhile, a Ukrainian court was expected to reach a verdict Monday for a Russian soldier who was the first to go on trial for an alleged war crime. The 21-year-old sergeant could get life in prison if convicted of shooting a Ukrainian man in the head through an open car window in a village in the northeastern Sumy region on Feb. 28, four days into the Russian invasion.

Ukrainian Prosecutor General Iryna Venediktova previously said her office was readying war crimes cases against 41 Russian soldiers for offenses that included bombing civilian infrastructure, killing civilians, rape and looting. Her office has said it was looking into more than 10,700 potential war crimes involving more than 600 suspects, including Russian soldiers and government officials.

(AP)