Ukrainian fighters who were holed up in a massive steel plant in the last known pocket of resistance inside the shattered city of Mariupol ignored a surrender-or-die ultimatum from Russia on Sunday and held out against the capture.

The fall of Mariupol, the site of a merciless 7-week-old siege that has reduced much of the city to a smoking ruin, would be Moscow's biggest victory of the war.

Russia would be able to secure a land corridor to the Crimean Peninsula and deprive Ukraine of a major port and its prized industrial assets if it were to capture the southern city.

Russia estimated that 2,500 Ukrainian troops and about 400 foreign mercenaries were dug in at the Azovstal steel mill, which covers more than 4 square miles, as missiles and rockets slammed into other parts of the country.

The head of the city's patrol police told Mariupol television that many Mariupol civilians, including children, are at the Azovstal plant. He said they are hiding from Russian soldiers.

Moscow gave the defenders a midday deadline to surrender, but the Ukrainians rejected it.

Ukrainian Prime Minister Denys Shmyhal said on This Week that they would fight to the end.

There was little hope of a military rescue of Mariupol on Sunday. Foreign Minister Dmytro Kuleba told CBS that the Ukrainian troops and civilians in Mariupol are surrounded. He said that the city doesn't exist anymore because of massive destruction.

The Lord's resurrection is a testimony to the victory of life over death, good over evil, said Ukrainian President Volodymyr Zelenskyy.

If Mariupol falls, Russian forces are expected to join an all-out offensive in the coming days for control of the Donbas, the eastern industrial region that the Kremlin is bent on capturing.

The Ukrainians estimate that at least 21,000 people have been killed in Mariupol. A maternity hospital was hit by a lethal Russian airstrike in the opening weeks of the war, and about 300 people were killed in the bombing of a theater where civilians were taking shelter.

The siege of Mariupol has left 100,000 people trapped without food, water, heat or electricity, making it the scene of some of the worst suffering of the war.

The spokesman for the Russian Defense Ministry said that all resistance will be destroyed.

The footage from the drones was carried by the Russian news agency RIA-Novosti and it showed a huge amount of smoke over the steel complex.

As Russian troops prepare for battle in the mostly Russian-speaking Donbas, where Moscow-backed rebels already control some territory, the Ukrainian deputy defense minister described Mariupol as a shield.

Russian forces carried out aerial attacks near Kyiv and elsewhere in an apparent effort to weaken the military capacity of Ukraine ahead of the assault.

After the sinking of the flagship of Russia's Black Sea Fleet last week in what the Ukrainians boasted was a missile attack, the Kremlin had vowed to step up strikes on the capital.

Russia said on Sunday that it had attacked an ammunition plant near Kyiv with precision-guided missiles, the third such strike in as many days.

Kramatorsk, the eastern city where rockets killed at least 57 people at a train station crowded with civilians trying to flee ahead of the Russian offensive, was hit by explosions overnight.

At least five people were killed by Russian shelling in the city of Kharkiv on Sunday. The streets were strewn with broken glass and debris from at least one rocket after the barrage slammed into apartment buildings.

Orthodox Palm Sunday is a sacred day and the Mayor of Kharkiv lashed out at Russian forces for not letting up the bombing campaign.

In his nightly address to the nation, Zelenskyy called the bombing in Kharkiv a deliberate terror.

A regional official in eastern Ukraine said at least two people were killed when Russian forces fired at residential buildings.

Zelenskyy called on the world to respond with more weapons and harsher sanctions after he said that Russian troops in southern Ukraine have been torturing and kidnapping people.

He said that torture chambers are built there.

Malyar, the Ukrainian deputy defense minister, said that the Russians continued to hit Mariupol with airstrikes and could be getting ready for an amphibious landing to reinforce their ground troops.

The upcoming offensive in the east would give Russian President Vladimir Putin a vital piece of the country and a badly needed victory that he could sell to the Russian people.

Austrian Chancellor Karl Nehammer is the first European leader to meet with Putin since the invasion.

In an interview on NBC's Meet the Press, Nehammer said he thinks Putin is winning the war and that we have to confront him.

There is a

Chernov was reporting from Kharkiv. Associated Press journalists around the world contributed to the report.

We can be reached at letters@time.com.