Another Russian attack a day earlier in Slovyansk, in eastern Ukraine, killed four and injured 16.
Both sides have continued attacks, even though the war has reached a stalemate recently.
Russia has been making slow advances in the battlefield, but Ukraine also says it is reclaiming more land seized by the Russians.
Zelensky says another round of talks – involving Russian and American negotiators – may be held next week.
The process is being led by US President Donald Trump, who has been trying to end the war.
The outcome of the talks hinges on part of his proposals that envisages Ukraine giving up to Russia areas it does not currently control in the Donbas – an industrial area composed of the administrative regions of Donetsk and Luhansk.
Russia currently controls more than 80% of those areas – which Ukraine says it cannot agree to relinquish.