KYIV, Ukraine--Ukrainians were digging in to defend the eastern city of Sievierodonetsk as it endured heavy bombardment from Russian forces trying to take the industrial area known as the Donbas.

In Tokyo on Monday, President Joe Biden, meeting with Japanese Prime Minister Fumio Kishida, thanked Japan for its strong leadership in standing up to Russia as the two united in condemning Moscow’s invasion of Ukraine.

Earlier on his trip to Asia, Biden signed legislation granting Ukraine $40 billion more in U.S. support for its defense against the Russian attack.

While Russian and Ukrainian forces battled along a 551-kilometer (342-mile) wedge of Ukraine’s eastern industrial heartland, Polish President Andrzej Duda traveled to Kyiv on Sunday to support Ukraine’s European Union aspirations and addressed Ukraine's parliament.

Duda received a standing ovation when he thanked the lawmakers for letting him speak where “the heart of a free, independent and democratic Ukraine beats.”

Ukraine does not have to yield to pressure from Russia and from elsewhere in Europe, Duda 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, a right-wing populist leader who clearly preferred the former U.S. president, Donald Trump, over Biden in the 2020 election, nonetheless said that “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.”

Poland has become an important ally of Ukraine, welcoming millions of Ukrainian refugees and becoming a gateway for Western humanitarian aid and weapons and a transit point for some foreign fighters who have volunteered to fight Russian forces.

Ukrainian President Volodymyr Zelenskyy called Duda's visit, his second since April, “a historic opportunity not to lose such strong relations, built through blood, through Russian aggression. All this not to lose our state, not to lose our people.”

Zelenskyy has urged the 27-member EU to expedite his country’s request to join. It is to be discussed at a Brussels summit in late June.

On the battlefield, grinding, town-by-town fighting continued as Russian troops try to expand the territory that Moscow-backed separatists have held since 2014 in the Donbas, which includes Luhansk and Donetsk.

Sievierodonetsk is the main city under Ukrainian control in Luhansk province, whose governor Serhii Haidai accused the Russians of “simply intentionally trying to destroy the city… engaging in a scorched-earth approach.”

Haidai said the Russians had occupied several towns and cities in Luhansk after indiscriminate, 24-hour shelling and were concentrating forces and weaponry there, bringing in troops from Kharkiv to the northwest, Mariupol to the south, and from inside Russia.

The sole working hospital in Sievierodonetck has only three doctors and supplies for 10 days, he said.

The Ukrainian military said Russian forces were unsuccessful in their attack on Oleksandrivka, a village outside the city.

To bolster its defenses, Ukraine’s parliament voted Sunday to extend martial law and mobilize its armed forces for a third time, until Aug. 23.

Ukrainian officials have said little since the war began about the extent of their country’s casualties, but Zelenskyy said at a news conference Sunday that 50 to 100 Ukrainian fighters were being killed, apparently each day, in the east.

In a general staff morning report, Russia said it was preparing to resume its offensive on Slovyansk, a city in Donetsk province that saw fierce fighting last month after Moscow’s troops backed away from Kyiv.

The conflict is not confined to Ukraine’s east. Powerful explosions were heard early Monday in Korosten, about 160 kilometers west of Kyiv, the town’s deputy mayor said. It was the third straight day of apparent attacks in the Zhytomyr District, Ukrainian news agencies reported.

In the Russian-held city of Enerhodar, 281 kilometers 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.

Also Monday, a Ukrainian court was expected to reach a verdict for the first Russian soldier standing trial for an alleged war crime. The 21-year-old sergeant, who has admitted to shooting a Ukrainian man in the head in the Sumy region on Feb. 28, could get life in prison if convicted.

Ukrainian Prosecutor General Iryna Venediktova said her office was prosecuting war crimes cases against 41 Russian soldiers for offenses that included bombing civilian infrastructure, killing civilians, rape and looting.

In other developments, Ukraine’s first lady, Olena Zelenska, gave a rare interview to national broadcaster ICTV alongside her husband and said she has hardly seen him since the war began.

“Our family, like all Ukrainian families, is now separated,” she said, adding that she speaks to him mostly by phone.

“Unfortunately, we cannot sit together, have dinner with the whole family, talk about everything,” she said.

Zelenskyy called the interview itself “a date on air,” and the couple, who have two children, joked in front of the journalists.

“We are joking, but we are really waiting, like everyone else, to be reunited, like all families in Ukraine who are separated now, waiting for their relatives and friends who want to be together again,” he said.