Embattled Ukraine Soldiers in Mariupol Say They Will Fight to the End

“We can’t just leave, we can only be evacuated,” said Lt. Ilia Samoilenko of Ukraine’s Azov Regiment in an online news conference from Azovstal. “We are basically dead men. Most of us know this.”

Western officials and analysts expect Russian President

Vladimir Putin

to use the World War II commemorations to address the war in Ukraine, possibly declaring victory or, in what some see as a more likely scenario, pledging to carry on the fight.

Mr. Putin might also call for a mass mobilization of Russia’s army and its citizens, some Western and Ukrainian defense and intelligence officials have speculated. The Kremlin has brushed off such talk as unfounded rumors.

In other developments Sunday, first lady Jill Biden made a surprise visit to Ukraine from neighboring Slovakia and met with

Olena Zelenska,

wife of President

Volodymyr Zelensky.

It was the first time Ms. Zelenska had been seen in public since the Russian invasion began in February.

Ukrainian authorities, meanwhile, said that a Russian airstrike was believed to have killed some 60 villagers who had taken refuge in a school in Ukraine’s Luhansk region.

In Mariupol, Azov Regiment leaders said thousands of civilians have perished after weeks of heavy Russian bombardment.

“The [Kyiv] government failed in the preparation of the defense of Mariupol…we feel abandoned,” said Lt. Samoilenko. “Nobody expected we would last so long, and we are still holding.”

A spokesman for Mr. Zelensky declined to comment, saying it was a question for the military to address. Mr. Zelensky has previously called on Russia to release or exchange those remaining at Azovstal.

“If they kill people who can be exchanged as prisoners of war or just released as civilians or be helped as wounded or injured, civilian and military alike, if they destroy them, I don’t think we can have any diplomatic talks with them after that,” he said in comments Friday.

Azov deputy commander Capt. Svyatoslav Palamar said more than 25,000 civilians have been killed in the Russian onslaught, which has lasted for well over two months.

“It is such a pity that some politicians of Ukraine are rather cynical because they say this was a successful evacuation of civilians,” he said.

He acknowledged that hundreds of civilians who were sheltering in the Soviet-era network of bunkers under the Azovstal steel plant have been evacuated, but said others might remain.

“Not a single international organization nor representative of politicians or governments has been here to help,” Capt. Palamar said.

The news conference, held via video link, was made possible by the internet access provided by Starlink, the satellite internet company that is a division of

Elon Musk’s

Space Exploration Technologies Corp., Ukraine officials said.

The Azov regiment and 100 marines are the only Ukrainians still fighting in Mariupol. They have killed more than 2,500 Russian troops and wounded many more, and destroyed 60 tanks, Lt. Samoilenko said.

The Azov regiment was formed from a far-right volunteer force. Mr. Putin has sought to exploit that to reinforce his claim that Russia is fighting Nazis in Ukraine—an assertion denounced by Mr. Zelensky, who is Jewish and points out that Ukrainians suffered heavily at the hands of the Nazis in World War II.

Kateryna Prokopenko, wife of Azov commander Col. Denys Prokopenko, said that she and other relatives of the trapped fighters want Mr. Zelensky to put pressure on Mr. Putin to release the Ukrainian troops.

“We don’t want all of them to die and then everyone to tell heroic stories about them,” Ms. Prokopenko said. She said her husband told her that some of the more than 200 wounded Azov fighters were dying of gangrene amid lack of medical care.

The Russian airstrike in the Luhansk region happened late Saturday in the village of Bilohorivka and hit a school and a nearby concert hall, causing a fire, authorities there said.

By the time the fire was extinguished hours later, rescuers had pulled out 30 survivors and found two bodies, while some 60 others who remain under the rubble are presumed dead, said Luhansk Gov.

Serhiy Haidai.

Ukraine’s rescue service said it would continue looking for possible survivors in Bilohorivka on Sunday.

Russian authorities didn’t immediately respond to a request for comment.

Russian forces have made significant advances in the Luhansk region in recent days, with the Wagner mercenary group taking most of the strategic town of Popasna and other troops inching closer to the capital of the Ukrainian-administered part of the region, Severodonetsk.

Only a small part of the region remains under Ukrainian control, and authorities have urged all civilians to leave.

Mr. Putin in February recognized the independence of the so-called Donetsk and Luhansk people’s republics, statelets created by Moscow in 2014 in the part of eastern Ukraine collectively known as Donbas.

After pulling forces from the vicinity of Ukraine’s capital, Kyiv, in late March, Mr. Putin declared what he called the liberation of Donbas as the war’s key goal. He later cited the seizure of the city of Mariupol as a major success.

While Russian forces are making slow but steady progress in the Donetsk and Luhansk regions, they have suffered significant setbacks in the Kharkiv region to the north.

In a counteroffensive, Ukrainian troops this weekend continued pushing north and northeast of Kharkiv, Ukraine’s second-most populous city, after ousting Russian forces from key towns in its immediate vicinity. At the same time, Ukrainian troops attacked the flank of the Russian troops advancing toward Donbas, striking west of the city of Izyum, according to reports from both sides.

Ukraine is also continuing its campaign to deny Russian forces the use of the strategic Snake Island southwest of the Black Sea port of Odessa. Russia captured the island on the first day of the war, Feb. 24.

The Ukrainian military, which struck two Raptor-class Russian patrol boats near the island last week, said this weekend it hit a Serna-type landing craft with an air-defense system aboard, and two more Raptor vessels. Drone footage released by the Ukrainian military showed a vessel exploding and an airstrike on the island by what appeared to be Ukrainian jet fighters.

Another video, released on Sunday, showed a drone strike hitting what appeared to be a Russian helicopter as troops were disembarking on the island.

Russia’s Defense Ministry said Sunday it destroyed four Ukrainian warplanes, four helicopters and a Ukrainian landing vessel near Snake Island. It offered no evidence. Ministry officials haven’t commented on the claimed Ukrainian strikes against the Russian navy.

Russia has also been hitting back by raining cruise missiles on infrastructure targets across Ukraine, particularly in the Odessa region.

On Sunday, Mr. Putin paid tribute to the soldiers and home-front workers of World War II, who he said had defended the nation from Nazism “at the cost of innumerable victims and hardships.”

“Today, the common duty is to prevent the revival of Nazism, which brought so much suffering to people from different countries,” Mr. Putin said in a statement published by the Kremlin. “It is necessary to preserve and pass on for posterity the truth about the events of the war years, common spiritual values and traditions of fraternal friendship.”

Mr. Putin has said he sent troops into Ukraine on grounds that the country’s leaders are neo-Nazis intent on harming Russian-speaking citizens of Ukraine, but he has provided no evidence to back that up.

Dr. Biden, who had been traveling in Romania and Slovakia, made a surprise appearance in the town of Uzhhorod in western Ukraine for a meeting with Ms. Zelenska in a small classroom. She told Ms. Zelenska that it was “important to show the Ukrainian people that this war has to stop.”

She is the latest high-profile U.S. official to enter Ukraine during its conflict with Russia, a list that has included Secretary of State

Antony Blinken

and House Speaker

Nancy Pelosi.

—Ann M. Simmons, Ken Thomas and Matthew Luxmoore contributed to this article.

Write to Bojan Pancevski at bojan.pancevski@wsj.com and Yaroslav Trofimov at yaroslav.trofimov@wsj.com