Fierce fighting continued in the eastern Donbas region, where President Volodymyr Zelenskiy said that Ukrainian forces were "holding on" despite Moscow concentrating its firepower there.

The fiercest fighting remains around the eastern industrial city of Syevyerodonetsk, a battle that Zelenskiy has said is pivotal for the fate of the Donbas region.

Ukrainian forces now control roughly one-third of the key city despite Russia throwing overwhelming numbers of troops and equipment into the battle, officials said.

Pro-Russian rebels said they had surrounded the Azot chemical plant in Syevyerodonetsk, trapping a small group of Ukrainian forces there.

Rodion Miroshnik, an official in what the separatists call the Luhansk People's Republic, said on Telegram that all escape routes had been cut off. Miroshnik acknowledged the possibility that civilians might still be sheltering at the besieged site.

Ukrainian Defense Ministry spokesperson Oleksandr Motuzyanyk said Russia is looking for weak points in Ukrainian defenses near the Siverskiy Donets river. He told national television on June 10 that Russian forces had not abandoned attempts to launch storming operations in the area.

Some areas of the Zaporizhzhya region have been placed under an extended curfew due to “active hostilities in the region and the real threat to life and security,” authorities said.

The curfew will run from 10 p.m. on June 11 to 5 a.m. on June 13 in the Vasylivka, Berdyansk, Melitopol, and Pologi districts.

The General Staff of the Armed Forces of Ukraine said in its evening report on June 10 that Russian troops launched air strikes on several towns in the Donetsk region using Su-25 aircraft, Ka-52 helicopters, and Mi-8 helicopters.

The General Staff said Russian units were preparing to resume an offensive on the eastern city of Slovyansk, firing artillery at several towns.

None of the reports on fighting could be independently verified.

Zelenskiy's senior aide Mykhaylo Podolyak said that, because of Russia's lopsided advantage in heavy artillery, Ukraine was losing between 100 and 200 soldiers daily on the front line.

The figure advanced by Podolyak was higher than a previous estimate by Defense Minister Oleksiy Reznikov, who on June 9 said Ukraine was losing 100 soldiers a day, and 500 more were wounded. The discrepancy in figures appears to indicate the difficulty of obtaining accurate battlefield information.

Podolyak told the BBC that Ukraine needed hundreds of Western artillery systems to level the playing field with Russia in the Donbas.

Ukraine also asked for humanitarian support to combat an outbreak of dysentery and cholera in the port city of Mariupol, which has been reduced to ruins.

Mayor Vadym Boychenko told national television that sanitation systems were broken and corpses were rotting in the streets.

"Unfortunately...these infection outbreaks will claim thousands more Mariupolites," Boychenko said.

He called on the United Nations and the International Committee of the Red Cross to work on setting up a humanitarian corridor to allow remaining residents to leave the city, which is now under Russian control.

Britain's Ministry of Defense said earlier on June 10 in its daily intelligence bulletin that there was a risk of a major cholera outbreak in Mariupol.

The bulletin said isolated cases of cholera have been reported in Mariupol since last month. British intelligence also assessed that Russia was struggling to provide basic public services to the inhabitants of the territories that it has occupied in Ukraine.

Ukraine and Russia have conducted another prisoner swap, Mykolayiv regional governor Vitaliy Kim said on Telegram. The exchange involved four Russian captives for five Ukrainians, including a village head who was "kidnapped" by Russian forces on March 10, he said.

With concern over Ukrainian grain deliveries growing by the day, an adviser to French President Emmanuel Macron said France was ready to assist in an operation to allow safe access to Ukraine's Black Sea port of Odesa.

With reporting by AFP, BBC, Reuters, dpa, and AP