Russian forces made significant gains in Ukraine on Saturday, advancing into the beleaguered port of Mariupol, destroying an underground weapons depot to the west and leaving a marine barracks in ruins following one of the rocket strikes the deadliest attacks on the Ukrainian military in the nearly month-long war. .

As the fighting raged, Ukraine faced a deepening humanitarian crisis and military casualties mounted on both sides. A senior Ukrainian military official said on Saturday that the strike on the barracks, which occurred in the southern city of Mykolaiv on Friday, killed more than 40 marines.

At the city morgue, the bodies of dozens of uniformed marines lay side by side in a storage area. A morgue worker did not specify the number of dead brought from the site of the attack.

“A lot,” said the employee. “I won’t say how many. But a lot.”

Credit…Bulent Kilic/Agence France-Presse — Getty Images

In addition, the Russian Defense Ministry said on Saturday that it had used a hypersonic missile for the first time to destroy an underground ammunition depot in the western region of Ivano-Frankivsk. Ukraine’s military spokesman confirmed the hit on Saturday, but said the type of missile was “still to be determined”.

If confirmed, the use by the Russian army of a new generation of its missiles, called Kinzhal or Dagger, would mark an escalation of the conflict. Hypersonic missiles are capable of flying at five times the speed of sound, according to military analysts.

On Saturday, Ukrainian President Volodymyr Zelensky called directly on Russians to support a diplomatic resolution to the war, and added a stern warning.

“I want everyone to hear me now, especially in Moscow,” Mr. Zelensky said in a video address hours after Russian President Vladimir V. Putin spoke to tens of thousands of Russians during a a rally in the biggest stadium in Moscow. “It’s time to meet, to talk. It is time to restore territorial integrity and justice for Ukraine. Otherwise, Russia’s losses will be so huge that several generations will not be enough to bounce back.

He repeated the Ukrainian army’s claim that 14,000 Russian soldiers had been killed. The Pentagon estimates the figure to be around half that figure, a still staggering tally that US officials say the Kremlin has sought to conceal.

“Just imagine, 14,000 corpses and tens of thousands of injured and maimed people in this stadium in Moscow,” Mr Zelensky said. “There are already so many Russian casualties as a result of this invasion. This is the price of war. In just over three weeks. The war must end.

Street battles erupted in Mariupol, the southeastern port city the Russians have besieged since the early days of the conflict, as Russian troops and allied irregular forces entered the city after weeks of devastating missile barrages which turned it into a wasteland of bombed-out buildings.

Residents who have fled the city in recent days have described scenes of dead bodies dotting the streets, widespread looting and the suffering endured by thousands of people who remain trapped without heat or water.

Credit…Maxar Technologies., via Associated Press

Corpses “lay in the street, just covered in rags,” said Eduard Zarubin, a doctor from Mariupol who escaped from the city on Wednesday. “No one cleaned up because there were no ambulances, or the ones still working had too much to do.”

A video shared by the pro-Russian leader of Russia’s Chechnya region, Ramzan Kadyrov, claimed to show Chechen fighters, known for their ruthless war tactics, inside Mariupol.

The New York Times has not independently verified the content of the video.

Mr Kadyrov claimed that thousands of fighters loyal to him were now fighting for Russia in Ukraine. However, some Chechen rebel leaders who fought for the region’s independence from Russia in the 1990s promised to join the fight alongside Ukraine.

Russia’s Defense Ministry said in a statement it was “tightening the noose” around Mariupol. And the Ukrainian government reported that its forces were outgunned, attempts to provide air support had failed and it had “temporarily” lost contact with city officials.

A recently evacuated resident said friends and family members who remained in the city told her that the Russian flag was already flying in some neighborhoods and that there were non-Ukrainian tanks and soldiers on the streets.

A city official, Pyotr Andryuschenko, said on Saturday that Russian forces had taken “between 4,000 and 4,500 residents of Mariupol by force across the border to Taganrog”, a city in southwestern Russia. Given the chaos in the city, his claim could not be independently verified, although it was supported by testimonies from others who had recently fled.

If Russian forces were to take Mariupol, it would be one of the few major cities they have taken and give them control of much of Ukraine’s southern coast. Sounding a note of resignation, an adviser to the Ukrainian president said on Friday: “There is no chance of lifting the siege of Mariupol.”

Credit…Reuters

Russian advances in Mariupol have hampered frantic efforts to find survivors from the rubble of a theater that was nearly flattened in an attack on Wednesday. About 130 people were rescued from the theater, according to Ukrainian officials, who estimated that hundreds of people, possibly as many as 1,300, could still be trapped in the basement.

Russian forces struck the theater, even though the word “children” was written in large white letters on the floor at each end of the building.

“These are barbaric methods,” said Mr. Zarubin, the Mariupol doctor. “I think it’s genocide.”

Even as Russian forces pushed into Mariupol, the Ukrainian army claimed to have recaptured towns and villages around Kherson, one of the first towns to fall. To the west, the Ukrainian military defense of the strategic city of Mykolaiv continued to hold, preventing a Russian advance on Odessa, a major port on the Black Sea. And a bloody battle for Kyiv, the capital, looms, as Ukrainian and Russian troops engage in heavy fighting in the suburbs.

In western Ukraine, a region that had been largely spared heavy fighting in the south and east, Russian forces stepped up their attacks on military targets.

Russia’s claim that it used a hypersonic missile in Ivano-Frankivsk came a day after its rockets hit a warplane repair plant near Lviv, rocking a western city that has been a haven for Ukrainians fleeing more besieged areas. And last Sunday, a Russian airstrike hit a military base just 18 kilometers from the border with NATO member Poland.

Fighting across Ukraine has led to the fastest exodus of European refugees since World War II. More than a fifth of the 44 million people who lived in Ukraine before Russia invaded last month have been internally displaced or fled to other countries, according to UN estimates.

And for those who remain in the country, millions face a daily struggle for survival as towns hard hit by fighting run out of food and clean water, and lack medical care, heat and water. ‘electricity.

Credit…Ivor Prickett for The New York Times

The United Nations on Friday completed its first humanitarian aid convoy to the hard-hit city of Sumy in eastern Ukraine, delivering what it said were medical supplies, food and water to 35 000 people.

“We hope this is the first of many shipments delivered to people trapped by the fighting,” said Amin Awad, the UN crisis coordinator in Ukraine.

As NATO prepares for a possible incursion into Allied countries, Norwegian authorities reported that four US Marines were killed on Friday when their Osprey plane crashed there during NATO exercises.

The cold weather drills, involving 30,000 troops from 25 countries in Europe and North America, have been announced more than eight months ago before the start of the war in Ukraine, NATO said. But they took on greater importance in the aftermath of the invasion.

With no clear diplomatic solution to the war and the death toll rising day by day, there has barely been time to mourn the losses in Ukraine. But in the heart of Lviv, residents have created a striking memorial: 109 empty strollers parked on the cobblestones of Rynok Square, meant to symbolize the 109 children who Ukrainian officials say were killed by Russian shelling.

A photo of the memorial, posted by Lviv Mayor Andriy Sadovy, was widely shared on Facebook.

“This is the terrible price of war that Ukraine is paying today,” Sadovy wrote.

Credit…Yuriy Dyachyshyn/Agence France-Presse — Getty Images

Michael Levenson reported from New York, Marc Santora of Warsaw and Valerie Hopkins from Lviv, Ukraine. The report was provided by Michael Schwirtz from Odessa, Ukraine; Victoria Kim of Seoul and Anatoly Kurmanayev from Mexico City.