KYIV, June 5 - Ukrainian fighters over the weekend pushed back Russian forces in the city of Sievierodonetsk that Moscow had focused on capturing to advance in the eastern region of Donbas, according to reports on Sunday.

The U.K. military said in its daily intelligence update that Ukrainian counterattacks in Sieverodonetsk were “likely blunting the operational momentum Russian forces previously gained through concentrating combat units and firepower.” Russian forces previously had been making a string of advances in the city.

The statement also said Russia’s military was partly relying on reserve forces of Luhansk separatists.

“These troops are poorly equipped and trained, and lack heavy equipment in comparison to regular Russian units,” the intelligence update said, adding that the move “indicates a desire to limit casualties suffered by regular Russian forces.”

In the Azov Sea port of Mariupol, which Russia claimed to have captured in May following a brutal monthslong siege, a mayoral aide said water supplies contaminated by decomposing corpses and garbage were causing dysentery and posing a threat of cholera and other diseases.

In remarks carried by Ukraine’s Unian news agency, Petro Andriushchenko said Russian authorities controlling the city have imposed a quarantine, The Associated Press reported. He did not describe what measures Russian authorities had included, and his report could not be independently confirmed.

World Health Organization officials warned last month about the threat of cholera and other infectious diseases in Mariupol.

Also Sunday, President Volodymyr Zelenskyy traveled to the Zaporizhzhia region in the southeast, which is partly under Russian control. He received a battle report, thanked troops and met with refugees in what was only his second public visit outside the Kyiv area since the war began. (ap/ez)