US President Donald Trump has renewed his sharp criticism of Volodymyr Zelensky, saying the Ukrainian leader is "more difficult to deal with than [Russian President Vladimir] Putin".
Speaking to US media on Thursday evening, Trump also called Ukraine's fresh wave of strikes on Russian oil refineries a "disgrace".
Zelensky, who is in Brussels for a summit with EU leaders, had paused the attacks for three days at Trump's request for a ceasefire on energy targets, but said on Thursday the strikes would resume because Moscow had never stopped.
Meanwhile, deadly attacks on Ukraine continued overnight, with several people killed in a Russian drone strike in the north-eastern city of Kharkiv, the regional governor said.
At least 14 people were injured, Oleg Synegubov wrote on Telegram.
Zelensky has not commented on Trump's latest criticism. He arrived at the summit in Brussels flanked by European Commission President Ursula von der Leyen and European Council President António Costa.
"Of course we supported President Trump's energy ceasefire but we've seen that Russia did not respect it, not a single minute," Von der Leyen told reporters. "Russia escalated and therefore we have to increase sanctions on Russia... We will not lift any sanctions unless Russia stops the war."
Trump's comments about Zelensky, during an interview with US outlet Newsmax, indicate the deteriorating relationship between the US and Ukraine.
"Zelensky is not a good guy for us to deal with," Trump said. "He doesn't want to settle. He says he wants to settle, but he doesn't," he added.
"I'm not a big fan of Zelenskyy".
When asked about Ukraine's renewed strikes on Russian oil refineries, Trump said it was "a disgrace".
"All he's doing is making the world oil price higher... There are a lot of targets that you can hit."
Trump is frustrated at Ukraine's continued targeting of Russian oil refineries because the US recently announced a deal to import 300,000 tonnes of Russian diesel to the American market, in an effort to bring down fuel prices.
That deal, in turn, infuriated Zelensky, who called it a gift to Putin.
Zelensky has been holding back-to-back talks with EU leaders while in Brussels. On Thursday he met Nato chief Marke Rutte, as well as the presidents of Poland, France, Denmark and Belgium.
A day earlier, he met UK Prime Minister Andy Burnham at No 10 in London.
At the summit on Friday, Zelensky said he would hold talks with the chiefs of the European Council and European Commission, and the prime ministers of Hungary, Finland, and Sweden.