Russian forces have resumed their assault on a sprawling steel factory in the devastated Ukrainian port of Mariupol, using aircraft to pound Ukrainian fighters holding out there.

A top Ukrainian official, meanwhile, said that a new effort to evacuate civilians from the grounds of the Azovstal steel plant has been hampered by Russian firing despite a UN-brokered cease-fire. An estimated 200 civilians are reported to be hiding in the complex, along with as many as 2,000 Ukrainian fighters.

Ukraine’s General Staff said in its daily assessment on May 6 that Russians were using aircraft as part of the renewed assault on the plant.

“There are many wounded, but they are not surrendering,” Ukrainian President Volodymyr Zelenskiy said on May 5 in his nightly video address. “They are holding their positions.”

Mariupol itself has been largely razed to the ground by weeks of street-to-street fighting and heavy bombardment. Azovstal has turned into a last stand for the Ukrainians troops struggling to prevent a complete Russian defeat of the city.

The fighting comes as Russia continues its offensive in the eastern Donbas, an offensive that has proceeded slowly and without major advances, as Ukrainian forces have blocked Russian movements and even regained territory.

The fight for Azovstal also comes amid speculation that Russian President Vladimir Putin wants a battlefield triumph that he can showcase on May 9 when Russia marks Victory Day — the anniversary of the defeat of Nazi Germany.

“The renewed effort by Russia to secure Azovstal and complete the capture of Mariupol is likely linked to the upcoming 9 May Victory Day commemorations and Putin’s desire to have a symbolic success in Ukraine,” the British Defense Ministry said in its May 6 daily assessment.

“This effort has come at personnel, equipment, and munitions cost to Russia. Whilst Ukrainian resistance continues in Azovstal, Russian losses will continue to build and frustrate their operational plans in southern Donbas,” the ministry said.

Losing Mariupol would deprive Ukraine of a vital port on the Sea of Azov. It would also give Russia the ability to establish a land corridor to the Crimean Peninsula and free up troops to fight elsewhere in the Donbas.

The Ukrainians holed up in Azovstal’s labyrinthine tunnels and industrial infrastructure have been posting videos and photographs to social media, appealing to the international community.

Soldiers are “dying in agony” due to the lack of proper treatment, Captain Svyatoslav Palamar, deputy commander of the Azov Battalion, said in a video address on May 5. He pleaded for international help to evacuate the civilians and wounded fighters there.

Andriy Yermak, a top adviser to Zelenskiy, said on May 6 that nearly 500 civilians had been evacuated from the city and the Azovstal plant as part of a United Nations-led effort.

“The next stage of rescuing our people from Azovstal is under way at the moment. Information about the results will be provided later,” Yermak said in a post on Telegram on May 6. Kyiv will “do everything to save all its civilians and military.”

However, Mariupol authorities later said that Russian forces had fired at a vehicle that was involved in the evacuation, killing at least one Ukrainian fighter and wounding six.

Russia did not immediately comment. Russia’s RIA news agency said its correspondent had seen a bus with 12 civilians leave the Azovstal complex, but the reports could not immediately be confirmed.

Russia’s renewed offensive in the Donbas — now in its third week — has been slow-going, amid stubborn defense from Ukrainian forces who are increasingly equipped with heavy artillery and powerful anti-tank and antiaircraft weaponry supplied from NATO members.

Germany, which has come under pressure at home and abroad to step up its equipment supplies, said on May 6 that it would supply seven self-propelled howitzers to Ukraine after reversing its policy not to send heavy armaments to war zones.

Earlier, Berlin announced it would also be sending “Gepard” antiaircraft systems.

The Donbas offensive came after a thwarted campaign by Russian forces north of Kyiv in the early weeks of the war. The withdrawal of Russian troops from places like Bucha, near Kyiv, has led to a cascade of reports from witnesses who say Russian units committed atrocities that could amount to war crimes.

Rights watchdog Amnesty International said on May 6 there was compelling evidence that Russian troops had committed war crimes, including extrajudicial executions of civilians, when they occupied an area outside Ukraine’s capital in February and March. Civilians also suffered abuses such as “reckless shootings and torture,” the group said.

Russian troops had committed a “host of apparent war crimes” in Bucha, including “numerous unlawful killings,” most of them near the intersection of Yablunska and Vodoprovidna streets, the report found.

With reporting by RFE/RL’s Ukrainian Service and AP