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

Lawmakers stood to applaud 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 Kyiv since April, came as Russian and Ukrainian forces battled along a 342-mile wedge of the country’s eastern industrial heartland.

After declaring full control of a sprawling seaside steel plant that was the last defensive holdout in the port city of Mariupol, Russia launched artillery and missile attacks in the region, known as the Donbas, seeking to expand the territory that Moscow-backed separatists have held since 2014.

To bolster its defenses, 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 his country’s request to join the bloc as soon as possible due to the invasion. Ukraine’s potential candidacy is set to be discussed at a Brussels summit in late June.

France’s European Affairs minister Clement Beaune on Sunday told Radio J it would be a “long time” before Ukraine gains EU membership, estimating it could take up to two decades.

“We have to be honest,” he said. “If you say Ukraine is going to join the EU in six months, or a year or two, you’re lying.”

But Poland is ramping up efforts to win over other EU members who are more hesitant about accepting the war-ravaged country into the bloc. 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 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,” Duda told the Verkhovna Rada, Ukraine’s legislature.

Duda also credited the U.S. and President Joe Biden for unifying the West in supporting Ukraine and imposing sanctions against Moscow.

“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. The Ukrainian military said Sunday that Russian forces had mounted an unsuccessful attack on Oleksandrivka, a village outside of Sievierodonetsk.

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

In a general staff morning report, Russia also said 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 away from Kyiv.

In Enerhodar, a Russian-held city 174 miles northwest of Mariupol, an explosion Sunday injured the Moscow-appointed mayor at his residence, Ukrainian and Russian news agencies reported. Ukraine’s Unian news agency said a bomb planted by “local partisans” wounded 48-year-old Andrei Shevchuk, whose home is near the Zaporizhzhia Nuclear Power Plant, which is Europe’s largest and employs many Enerhodar residents.

With Russia claiming to have taken prisoner nearly 2,500 Ukrainian fighters from the 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 feared dead.