The two cities nestled in the Donbas industrial heartland of Ukraine are being bombarded by heavy Russian shelling and fierce street-to-street battles have broken out between invading troops and fighters loyal to Kyiv.
Fourteen weeks into the invasion, Moscow is pushing to capture the cities so it can take full control of the Luhansk region and tout it as a war victory.
A Ukrainian official on Tuesday said street fighting continued to rage in the flashpoint city of Severodonetsk and that the situation was changing “every hour”.
Just days ago, Moscow seemed close to taking the strategic industrial hub but Ukrainian forces have managed to stand their ground.
Mr Zelenskyy has warned his troops in the city are outnumbered by Russian forces.
Speaking to journalists in Kyiv on Monday, Mr Zelenskyy said “we’re holding out” in Severodonetsk but “there are more of them and they are stronger”, adding that the key city and its neighbouring hub of Lysychansk were “dead cities”.
“Our heroes are holding their positions in Severodonetsk,” the president said in a video address on Monday evening. “Fierce street fights continue in the city.”
Mr Zelenskyy on Sunday visited Lysychansk where he met civilians and fighters.
Local resident Olexsandr Lyakhovets told AFP that shortly after the president’s departure a Russian missile hit his apartment block. “They shoot here endlessly,” Mr Lyakhovets said. “It's a horror show.”
Severodonetsk — the largest city still in Ukrainian hands in the Lugansk region of the Donbas — has been the focal point in recent weeks, and officials describe a fast-changing situation on the ground.
“The situation is changing every hour, but at the same time there are enough forces and resources to repel attacks,” said mayor Oleksandr Striuk on Monday.
“We have hope, we have faith in our armed forces, no one's going to abandon” Severodonetsk, he added.
Russia is planning to cut off the Severodonetsk area from the north and the south in a bid to capture the key city, British intelligence suggests.
In an update issued on Twitter on Tuesday, the UK’s Ministry of Defence (MoD) said Ukrainian forces had recaptured some territory in the city at the weekend, “although Russian forces likely continue to occupy eastern districts”.
“Russia’s broader plan likely continues to be to cut off the Severodonetsk area from both the north and the south,” the MoD added.
Moscow has made gains in Popasna, a town south of Severodonetsk, the MoD said, but its progress in the area has hit a brick wall in recent weeks.
There has been heavy shelling around Izium, a city in the Kharkiv oblast (region) of eastern Ukraine, suggesting “Russia is preparing to make a renewed effort on the northern axis.”
“Russia will almost certainly need to achieve a breakthrough on at least one of these axes to translate tactical gains to operational level success and progress towards its political objective of controlling all of Donetsk oblast,” the MoD added.