Russian forces pushed deeper into Ukraine’s besieged and battered port city of Mariupol on Saturday, where heavy fighting shut down a major steel plant and local authorities pleaded for more Western help.

The fall of Mariupol, the scene of some of the war’s worst suffering, would mark a major battlefield advance for the Russians, who are largely bogged down outside major cities more than three weeks into the biggest land invasion in Europe since the Second World War.

“Children, elderly people are dying. The city is destroyed and it is wiped off the face of the earth,” Mariupol police officer Michail Vershnin said from a rubble-strewn street in a video addressed to Western leaders that was authenticated by the Associated Press.

Russian forces have already cut the city off from the Sea of Azov, and its fall would link Crimea, which Russia annexed in 2014, to territories controlled by Moscow-backed separatists in the east. It would mark a rare advance in the face of fierce Ukrainian resistance that has dashed Russia’s hopes for a quick victory and galvanized the West.

Ukrainian and Russian forces battled over the Azovstal steel plant in Mariupol, Vadym Denysenko, adviser to Ukraine’s interior minister, said on Saturday. “One of the largest metallurgical plants in Europe is actually being destroyed,” Denysenko said in televised remarks.

Oleksiy Arestovych, an adviser to Ukraine’s president, said the nearest forces that could assist Mariupol’s defenders were already struggling against “the overwhelming force of the enemy” or at least 60 miles away.

“There is currently no military solution to Mariupol,” he said late on Friday. “That is not only my opinion, that is the opinion of the military.”

Ukrainian president Volodomir Zelensky has remained defiant, appearing in a video early on Saturday shot on the streets of the capital, Kyiv, to denounce a huge Friday rally in Moscow that Russian president Vladimir Putin attended.

Zelensky said Russia is trying to starve Ukraine’s cities into submission but warned that continuing the invasion would exact a heavy toll on Russia. He also repeated his call for Putin to meet with him to prevent more bloodshed.

“The time has come to restore territorial integrity and justice for Ukraine. Otherwise, Russia’s costs will be so high that you will not be able to rise again for several generations,” he said.

Putin lavished praise on his country’s military during the rally, which took place on the anniversary of Russia’s 2014 annexation of Crimea. The event included patriotic songs such as “Made in the U.S.S.R.,” with its opening line of “Ukraine and Crimea, Belarus and Moldova, it’s all my country.”

“We have not had unity like this for a long time,” Putin told the cheering crowd.

Meanwhile, fighting raged on multiple fronts in Ukraine. UN bodies have confirmed more than 847 civilian deaths since the war began, though they concede the actual toll is likely much higher. The U.N. says more than 3.3 million people have fled Ukraine as refugees.