Heavy fighting continued to rage Thursday within the depths of the demolished steel mill in Mariupol as Russian forces attempted to overpower the last defenders of the vital Ukrainian port city and complete its capture.

The bloody battle came amid growing speculation that President Vladimir Putin wants to present the Russian people with a major battlefield success – 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 in the tunnels and bunkers under the sprawling Azovstal steelworks in Mariupol, 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.

Capt. Sviatoslav Palamar, who as deputy commander of Ukraine's Azov Regiment led defenders inside the mill, told Ukrainian TV that Russian troops were inside the plant for a third day and meeting fierce resistance.

"Heavy fighting is underway," Palamar said.

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.

Mariupol’s fall would be a major success for Moscow, depriving Ukraine of a vital port, allowing Russia to establish a land corridor to the Crimean Peninsula, which it seized from Ukraine in 2014, and freeing up troops to fight elsewhere in the Donbass, the eastern industrial region that the Kremlin says is now its chief objective.

Palamar pleaded with the world to pressure Russia into allowing more civilians to be rescued from the steelworks along with wounded fighters. About 100 civilians were evacuated over the weekend.

"Wounded soldiers are dying in agony due to the lack of proper treatment," he said via video.

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

Kateryna Prokopenko, the wife of Azov Regiment commander Denys Prokopenko, said that without an evacuation operation by European leaders, the troops inside will die.

"They stand till the end. They only hope for a miracle. ... They won’t surrender," she said in messages to The Associated Press (AP). She said that in a call with her husband, he said he would love her forever.

"I am going mad from this. It seemed like words of goodbye," she said. "They have held out too long and deserve to be saved."

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 Donbass.

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' President Alexander Lukashenko defended Russia’s invasion of Ukraine in an interview with AP 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 it 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 spokesperson 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 multiple rocket launchers near the southern city of Mykolaiv.

Five people were killed and at least 25 wounded in the shelling of cities in Donbass over the past 24 hours, Ukrainian officials said. The attacks damaged houses and a school.

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 Donbass.

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.