President Donald Trump on Saturday criticized Volodymyr Zelensky as the two sparred over a new US-Russia diesel deal, saying he would “suggest” Ukraine get a new leader.

“You know what I suggest? I suggest they get a new leader who can make a deal because he could have made many deals and for some reason, he never does,” Trump told reporters at the White House.

Zelensky, meanwhile, has slammed the agreement between the US and Russia, casting the new deal as an “investment in a war that must be ended, not prolonged.”

Trump had been fuming at Zelensky over Ukrainian attacks on Russian refineries before he struck the deal, a US official said. The official said the US repeatedly asked Ukraine to halt its attacks on Russian diesel refineries, to no avail.

The back-and-forth between the leaders, who have long had a tumultuous relationship, came after Trump said Friday that he secured a deal from his Russian counterpart, Vladimir Putin, to supply markets with Russian diesel fuel as he works to bring down energy costs ahead of the midterm elections. Ukraine’s continued refinery attacks were part of what led Trump to strike the deal, according to the US official.

Trump wrote on social media that Putin agreed in a call to “immediately supply” more than 300,000 tons of diesel to global energy markets, with another 500,000 tons promised in November. Together, the amounts — equal to 6 million barrels of diesel fuel — would cover about a day and a half worth of US demand, according to the US Energy Information Administration.