Two national guard visit the grave of a late soldier in Kharkiv cemetery, eastern Ukraine. [Photo Credit: AP News]

Russia pressed its offensive in eastern Ukraine on Sunday as Poland’s president travelled 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 gave a standing ovation to President Andrzej Duda, who thanked them for the honour of speaking where “the heart of a free, independent and democratic Ukraine beats.” Duda 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 551-kilometre (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 to expand the territory that Moscow-backed separatists have held since 2014 in the region known as the Donbas.

To bolster its defences, 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. 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, perhaps 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 EU members who are more hesitant about accepting Ukraine 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 into Ukraine. It is also a transit point for some foreign fighters who have volunteered to fight the Russian forces.

Duda 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 in the 2020 election.

In Enerhodar, a Russian-held city 281 kilometres (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, who lives near the Zaporizhzhia Nuclear Power Plant, Europe’s largest.

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

Relatives of the fighters have pleaded for them to be given rights as prisoners of war and eventually returned to Ukraine. Deputy Prime Minister Iryna Vereshchuk said Ukraine “will fight for the return” of every one of them.

Denis Pushilin, the pro-Kremlin head of the self-proclaimed Donetsk People’s Republic, vowed that the Ukrainian fighters from the plant would face tribunals.

The complete seizure of the Azovstal steel plant, a symbol of Ukrainian tenacity, gave Putin a badly wanted victory in the war he began nearly three months ago, on Feb. 24. 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.