Trump made the remarks in an interview with US outlet Newsmax on Thursday evening, in which he also described Ukraine's fresh strikes on Russian oil refineries as a "disgrace".
Zelensky, who has not commented on the criticism, arrived at a summit in Brussels flanked by European Commission President Ursula von der Leyen and European Council President António Costa.
Speaking to reporters, von der Leyen said: "Of course we supported President Trump's energy ceasefire but we've seen that Russia did not respect it, not a single minute. Russia escalated and therefore we have to increase sanctions on Russia... We will not lift any sanctions unless Russia stops the war."
The remarks came as Ukraine confirmed that its strikes on Russian refineries would resume, after pausing them for three days at Trump's request. Zelensky said the pause was intended to support a ceasefire on energy targets, but that Moscow had never stopped.
Meanwhile, deadly attacks on Ukraine continued overnight. The regional governor of Kharkiv, Oleg Synegubov, said several people were killed in a Russian drone strike on the north-eastern city, with at least 14 people injured.