The bloody battle came amid growing suspicions 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.
Ten 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, as Moscow struggles to gain momentum in the Donbas, the eastern industrial heartland that the Kremlin says is now its chief objective.
In the most searing example of how Ukrainian forces have slowed Russia's progress, Ukrainian fighters _ 2,000, by the Russians' estimate in recent weeks _ 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 inside the plant.
Ukraine said its fighters drove back a Russian thrust on the plant, which was also being heavily bombed from above. Videos shared online appeared to show the steel mill targeted by intense shelling at dawn.
``The Russian troops entered the territory of Azovstal but were kicked out by our defenders,'' Oleksiy Arestovych, an adviser to President Volodymyr Zelenskyy, said on Ukrainian television. ``We can say that the fighting is ongoing.''
The Kremlin denied its troops were storming the plant.
A Ukrainian officer leading defenders inside the last Mariupol bastion pleaded with the world to pressure Russia into allowing more civilians to be rescued along with wounded troops. About 100 civilians were evacuated over the weekend.
``Wounded soldiers are dying in agony due to the lack of proper treatment,'' Capt. Sviatoslav Palamar, deputy commander of the Azov Regiment, said in a video statement.
Mariupol's fall would be a major battlefield 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 Donbas.
Some analysts have suggested Putin may use Victory Day to expand what he calls the ``special military operation'' and declare all-out war. That would allow the Russian leader to introduce martial law and mobilize reservists to make up for significant troop losses. The Kremlin has dismissed such speculation.
Ahead of Victory Day, the southeastern city of Zaporizhzhia, a key transit point for evacuees from Mariupol, announced a curfew that would be in force from Sunday evening through Tuesday morning. Similar long curfews have been put in place in other Ukrainian cities near the front lines for fear of attacks.
In other developments, Belarus' authoritarian president, Alexander Lukashenko, defended Russia's invasion of Ukraine in an interview Thursday 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 in the interview, in which he seemed to direct his comments to the West, he 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.
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 forces shelled elsewhere in the Donbas and kept up their bombardment of railroad stations and other supply-line targets across the country to try to disrupt the supply of Western arms, which have been critical to Ukraine's defense.
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.
Five people were killed and at least 25 wounded in shelling of cities in the Donbas over the past 24 hours, Ukrainian officials said. The attacks damaged houses and a school.
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, 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.
Belarus announced the start of military exercises Wednesday, stirring fears that the Russian ally might jump into the war. Britain's Defense Ministry said that it does not believe the drills pose any immediate threat to Ukraine but that they could be used to tie down Ukrainian forces in the north and prevent them from joining the battle for the Donbas.