Donald Trump may walk away from the Ukrainian war, the US president’s oldest son has said in comments to a Middle East conference.

In a lengthy tirade against the purpose of continued fighting in Ukraine, Donald Trump Jr also said Ukraine’s “corrupt” rich had fled their country leaving “what they believed to be the peasant class” to fight the war.

Trump Jr has no formal role inside his father’s administration, but is a key figure in the Maga movement. His intervention reflects the antipathy among some inside the Trump team towards the Ukrainian government, and comes as Trump’s negotiating team is putting pressure on Kyiv to give up territory.

Trump Jr said the Ukrainian president, Volodymyr Zelenskyy, was prolonging the war because he knew he would never win an election if it ended. He said Zelenskyy was a borderline deity on the left, but argued that Ukraine was far more corrupt than Russia.

He also railed at the EU’s foreign policy chief, Kaja Kallas, saying European sanctions were not working since they had simply increased the price of oil, from which Russia could pay for its war. He described the European plan as “we are going to wait for Russia to go bankrupt – that is not a plan”.

He said he had only encountered three people during his canvassing of voters in the 2022 election campaign who thought the Ukraine war was a top-10 issue. The risk of Venezuelan boats bringing the drug fentanyl into the US was, he said, “far more a clear and present danger than anything that is going on in Ukraine or Russia”.

Trump Jr claimed, without providing evidence, that he had observed this summer on a single day in Monaco that 50% of the supercars such as Bugattis and Ferraris had Ukrainian number plates. “Do you think that was earned in Ukraine?” he asked.

“We hear all the rumours about what is going on when we see every licence plate in Monaco is Ukrainian […] the rich fled and they left what they believed to be the peasant class to fight these wars. There was no incentive to stop because long as the money train was coming and they were stealing, no one was auditing anything so there was no reason to come to peace.”

Asked if it was possible his father – who ran for election claiming he could bring peace to Ukraine – would simply walk away, Trump Jr said maybe, explaining his father is one of the most unpredictable people in politics. He vowed that the US was no longer going to be “the idiot with the chequebook”.