French, German and Italian Leaders to Meet With Zelensky in Kyiv

News of the planned meeting came as Ukrainian officials said Russia had made fresh gains in its efforts to encircle and capture the city of Severodonetsk, which would bring Moscow significantly closer to its goal of controlling the Donbas area in the country’s east, its foremost target recently in the war.

Serhiy Haidai,

the Ukrainian governor of the Luhansk region, which includes Severodonetsk, said on Sunday that Russians had destroyed a second bridge connecting Severodonetsk to Lysychansk, a Ukrainian stronghold just across the Siverskyi Donets river. Russian forces also shelled a chemical plant in the city’s industrial section, where civilians had taken shelter in bunkers, Mr. Haidai said.

The battlefield advances were the latest evidence that Russia is outgunning Ukrainian forces, using its superior artillery power to steadily take territory. Its gains have thrown added focus onto Ukraine’s pleas for more powerful and longer-range artillery and other weaponry from the West, as well as on Ukraine’s lack of capacity to manufacture ammunition for the Soviet-era heavy weapons in its arsenal.

Ukrainian officials warn that a defeat in the Donbas region would open the path for Russia to move on to additional parts of Ukraine and potentially back to Kyiv. Already, Moscow has moved to solidify its administrative control of occupied territories. It has recognized the independence of separatist regions in Donbas and has begun issuing Russian passports to some parts of the country ahead of expected referendums that would lead to annexing territory to Russia.

On Sunday, Mr. Haidai said that Ukrainian forces remained in control of the part of Severodonetsk that includes the Azot chemical plant, and he denied that residents were trapped inside. Rodion Miroshnik, an official for the pro-Russian breakaway region that calls itself the Luhansk People’s Republic, made that assertion Saturday, saying on the Telegram social-media platform that hundreds of Ukrainian fighters and civilians were stuck in bunkers underneath the plant.

The competing claims came as Russian forces kept up their efforts to take the city, the largest remaining outpost in Luhansk that Moscow hasn’t captured.

“No one is trapped in the plant,” Mr. Haidai said on Ukrainian television Sunday. “There are no battles on the site of the plant, just in the area nearby. The only thing is that they constantly shell this plant.”

For several weeks, Moscow has poured resources into taking Severodonetsk, the administrative capital of the Luhansk region, which together with Donetsk makes up the Donbas area. A majority of the city’s buildings have now been destroyed, and most residents have fled. But Ukraine has managed to hold on to the southern section of the city, according to the British Ministry of Defense.

Last week, a top aide to Mr. Zelensky said that his side was losing up to 200 fighters a day, largely due to the overwhelming Russian advantage in firepower. Over the weekend, Kyiv kept up its pleas for the West to send more advanced weapons—and to send them faster. Severodonetsk Mayor Oleksandr Stryuk said that Ukrainian defenders need long-range artillery and air defense systems to stop Russian troops from further advancing in Luhansk.

This week’s planned meeting among the leaders of France, Germany, Italy and Ukraine comes amid a split within NATO about what kind of military aid to send to Kyiv. France, Germany and Italy haven’t been sending large quantities of heavy weapons, while the U.S. and the U.K. have both pledged in recent weeks to send more advanced rocket-launching systems. Poland has dispatched over 200 main battle tanks and scores of heavy artillery pieces.

Mr. Scholz’s government has come under criticism from Ukraine, Western allies and the opposition at home for failing to provide more military support for Kyiv. Germany has committed to send self-propelled howitzer guns and antiaircraft tanks, among other advanced weaponry. However, none of the shipments have arrived yet, and some aren’t expected before late in the year. In contrast, Berlin provided substantial quantities of lighter, defensive weapons such as antitank and antiaircraft missiles.

Mr. Scholz also courted criticism by stating that he would not travel to Kyiv for a mere photo opportunity. The agenda of this week’s meeting couldn’t be learned.

Other European leaders, including British Prime Minister

Boris Johnson,

have already visited Kyiv in shows of support for Ukraine’s struggle against Russian aggression. U.S. first lady Jill Biden also visited Mr. Zelensky, along with Secretary of State

Antony Blinken

and other senior U.S. officials.

The battle to control Severodonetsk and the broader Donbas has been costly for Russia. Its slow progress in gaining territory has forced Moscow to again reassess its military plans in expectation of a longer war, according to Ukrainian intelligence. The Institute for the Study of War, a Washington, D.C., think tank, wrote that Vadym Skibitsky, the deputy head of the Ukrainian Main Intelligence Directorate, had said he had information that Russian forces were now planning for the fighting to extend into October.

The British Defense Ministry said Moscow had been firing heavy, 1960s-era antiship missiles against land targets, likely because its forces were running low on more precise, modern missiles.

“Do you remember how Russia hoped to capture the entire Donbas in early May?” Mr. Zelensky said in a video posted late Saturday. “It is already the 108th day of the war, it is already June. Donbas is holding on. The losses suffered by the occupiers, including in this area, are extremely significant.”

Mr. Zelensky said that Ukrainian forces were also winning back territory that Russians had occupied in the southern Kherson region.

Mr. Zelensky has continued his push for the European Union to add Ukraine as a member.

Ursula von der Leyen,

president of the European Commission, met with Mr. Zelensky in Kyiv on Saturday.

After the meeting, she said the commission would work with Ukraine to rebuild and draw new investment, and that it would have a response by the end of next week about the country’s ambitions to join the EU.

“Ukraine was already on a good track before the horrible and atrocious invasion,” she said.

Mr. Zelensky, in his Saturday night address, stressed that joining the EU was essential for his country.

“What else needs to happen in Europe to make it clear to skeptics that the very fact of keeping Ukraine outside the European Union works against Europe?” he said. “We will continue to work even harder at all levels to get the right decision.”

—Anastasiia Morozova contributed to this article.

Write to Ian Lovett at ian.lovett@wsj.com and Bojan Pancevski at bojan.pancevski@wsj.com