Zelenskiy added that Ukraine is seeing "a build-up of Russian forces for new strikes on the Donbas and we are preparing for that."
The Donbas region encompasses two self-proclaimed "people's republics" that Russia says it is helping to free from Ukrainian control.
The leader of the Donetsk People's Republic, Denis Pushilin, said on Wednesday that offensive operations were intensifying.
Donetsk includes the besieged port city of Mariupol, which has seen some of the war's heaviest fighting and bombardment and where about 170,000 people are trapped with scarce food and water.
"We cook what we find among neighbours. A bit of cabbage, a bit more of potatoes, we've found tomato paste, some beetroot," said former steel worker Viktor from Mariupol. They cook using a rudimentary barbecue and sleep in a basement, which he termed their "peaceful oasis."