LVIV, Ukraine (AP) — Ukrainian fighters in the tunnels underneath Mariupol’s pulverized steel plant held out against Russian troops Thursday in an increasingly desperate and perhaps doomed effort to deny Moscow what would be its biggest success of the war yet: the full capture of the strategic port city.

The bloody battle came amid growing speculation that President Vladimir Putin wants to present the Russian people with a battlefield triumph — or announce an escalation of the war — in time for Victory Day on Monday. That is the biggest patriotic holiday on the Russian calendar, marking the Soviet Union’s triumph over Nazi Germany.

Some 2,000 Ukrainian fighters, by Russia’s most recent estimate, were holed up at Mariupol’s sprawling Azovstal steelworks, the last pocket of resistance in a city largely reduced to rubble over the past two months. A few hundred civilians were also believed trapped there.

Kateryna Prokopenko, the wife of Azov Regiment commander Denys Prokopenko, a leader of the steel plant’s defenders, said that in a call with her husband from inside, he told he would love her forever.

“I am going mad from this. It seemed like words of goodbye,” she said.

Capt. Sviatoslav Palamar, deputy commander of the regiment, told Ukrainian TV that Russian troops were inside the plant for a third day and were meeting fierce resistance, noting that “heavy fighting is underway.”

The Russians managed to get inside with the help of an electrician who knew the layout, said Anton Gerashchenko, an adviser to Ukraine’s Internal Affairs Ministry.

“He showed them the underground tunnels which are leading to the factory,” Gerashchenko said in a video posted late Wednesday. “Yesterday, the Russians started storming these tunnels, using the information they received from the betrayer.”

The Kremlin denied its troops were storming the plant.

Additionally, the bombing of Mariupol theatre, which civilians were used as shelter, is much worst than previously thought according to new reports.

Already the deadliest known attack against civilians, the death toll is now estimated around 600 — double original estimates.

“We tried to do it based on the density, based on the people we know were in the building,” an AP reporter tracking the tolls told NewsNation’s “Rush Hour” Thursday.

The figure was determined by an Associated Press investigation which used floor plans, survivor testimony and accounts from rescuers.

The fall of Mariupol would deprive Ukraine of a vital port, allow Russia to establish a land corridor to the Crimean Peninsula, which it seized from Ukraine in 2014, and free up troops to fight elsewhere in the Donbas, the eastern industrial region that the Kremlin says is now its chief objective.

Palamar pleaded for the evacuation of civilians and wounded fighters from the steelworks, saying soldiers were “dying in agony due to the lack of proper treatment.”

The Kremlin has demanded the troops surrender. They have refused. Russia has also accused them of preventing the civilians from leaving.

The defenders will “stand till the end. They only hope for a miracle. … They won’t surrender,” the Azov commander’s wife said.

The head of the United Nations said another attempt to evacuate civilians from Mariupol and the plant was underway. U.N. Secretary-General Antonio Guterres said: “We must continue to do all we can to get people out of these hellscapes.”

More than 100 civilians were rescued from the steelworks over the weekend. But many previous attempts to open safe corridors from Mariupol have fallen through, with Ukraine blaming shelling and firing by the Russians.

Additionally, new reports reveal that 300 civilians were evacuated from Mariupol Thursday as Russian troops continue their attack.

Meanwhile, 10 weeks into the devastating war, Ukraine’s military claimed it recaptured some areas in the south and repelled other attacks in the east, further frustrating Putin’s ambitions after his abortive attempt to seize Kyiv. Ukrainian and Russian forces are fighting village by village.

The head of Britain’s armed forces, Chief of the Defense Staff Adm. Tony Radakin, said Putin is “trying to rush to a tactical victory” before Victory Day. But he said Russian forces are struggling to gain momentum in the Donbas.

Radakin told British broadcaster Talk TV that Russia is using missiles and weapons at such a rate that it is in a “logistics war” to keep supplied. He added: “This is going to be a hard slog.”

Fearful of new attacks surrounding Victory Day, the mayor of the western Ukrainian city of Ivano-Frankivsk urged residents to leave for the countryside over the long weekend and warned them not to gather in public places.

And the southeastern city of Zaporizhzhia, a key transit point for evacuees from Mariupol, announced a curfew from Sunday evening through Tuesday morning.

In other developments, Belarus’ authoritarian president, Alexander Lukashenko, defended Russia’s invasion of Ukraine in an interview with The Associated Press but said he didn’t expect the conflict to “drag on this way.”

Lukashenko, whose country was used by the Russians as a launch pad for the invasion, said Moscow had to act because Kyiv was “provoking” Russia.

But he also created some distance between himself and the Kremlin, repeatedly calling for an end to the conflict and referring to it as a “war” — a term Moscow refuses to use. It insists on calling the fighting a “special military operation.”

Mariupol, which had a prewar population of over 400,000, has come to symbolize the misery inflicted by the war. The siege of the city has trapped perhaps 100,000 civilians with little food, water, medicine or heat.

As the battle raged there, Russian Defense Ministry spokesman Maj. Gen. Igor Konashenkov said Russian bombardment Thursday hit dozens of Ukrainian military targets, including troop concentrations in the east, an artillery battery near the eastern settlement of Zarozhne, and rocket launchers near the southern city of Mykolaiv.

Five people were killed in shelling of cities in the Donbas over the past 24 hours, Ukrainian officials said. The attacks damaged houses and a school.

A missile attack on the eastern city of Kramatorsk wounded 25 people and damaged more than 800 apartments, two schools, a kindergarten and a medical institution, Pavlo Kyrylenko, the regional governor, said in a Telegram post. His post showed images of many buildings reduced to rubble.

Ukrainian forces said they made some gains on the border of the southern regions of Kherson and Mykolaiv and repelled 11 Russian attacks in the Donetsk and Luhansk regions that make up the Donbas.

The Washington-based Institute for the Study of War said that Ukrainian forces “have largely stalled Russian advances in eastern Ukraine,” and intensified Russian airstrikes on transportation infrastructure in the western part of the country have failed to stop Western aid shipments to Ukraine.

With the challenge of mine-clearing and rebuilding after the war in mind, Ukrainian President Volodymyr Zelenskyy announced the launch of a global fundraising platform called United24.

At the same time, Poland hosted an international donor conference that raised $6.5 billion in humanitarian aid. The gathering was attended by prime ministers and ambassadors from many European countries, as well as representatives of nations farther afield and some businesses.

In addition, a Ukrainian cabinet body began to develop proposals for a comprehensive postwar reconstruction plan, while Zelenskyy also urged Western allies to put forward a program similar to the post-World War II Marshall Plan plan to help Ukraine rebuild.