Regional governor of the eastern Luhansk region Serhiy Haidai said fighting in the area had intensified and the city feared becoming another Mariupol.
He reported on Telegram that Russian shelling in Severodonetsk and nearby Lysychansk had “increased tenfold”, with President Zelensky travelling to Lysychansk last Sunday that saw him get as close to the fighting as he had done since March.
Severodonetsk is the last city in the Luhansk region still under Ukrainian control, as Putin’s forces double down in their efforts to capture the city.
Kyiv’s troops successfully forced Russia out of the city centre in a counter-attack over the weekend, as a number of cities have changed hands over the course of the fighting.
Mr Haidai said: “The fighting is very dynamic.
“Half of the city was recaptured during the counteroffensive, but we are now holding positions in the industrial zone.
“Our defenders managed to undertake a counter-attack for a certain time; they liberated almost half of the city.
“But now the situation has worsened a little for us again.”
Mr Haidai also warned that Putin was “levelling Severodonetsk and Lysychansk to the ground”.
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“We brought confidence. I am proud of everyone with whom I met, whom I shook hands with.”
Russian forces have also targeted Kyiv with cruise missile strikes for the first time since April, injuring one person as they hit a railway site near the capital.
Putin has vowed to increase his military efforts over the supply of long-range missiles to Ukraine from the US and UK.