US President Donald Trump has said he thinks "it's time for Ukraine to get a new president" as he responded to Volodymyr Zelensky's criticism of the US diesel deal with Russia.

Zelensky warned a new deal to release millions of tonnes of Russian diesel into the US would provide Moscow with money to continue its war in Ukraine.

Speaking to the media as he left the White House on Saturday, Trump said the Ukrainian president "wants to make problems for the world" by continuing to authorise attacks on Russian refineries.

"He'd better damn well stop," Trump said before suggesting Ukraine should "get a new leader who can make a deal".

Russia and Ukraine have recently intensified their strikes, targeting energy-generating and transport facilities, as well as major logistics hubs.

"We said, 'you can do whatever you want to Russia, don't hit the refineries', because that's a world problem that's caused," he said.

"He could have made many deals and for some reason, he never does."

Trump confirmed on Friday that an agreement had been reached with Moscow to suspend sanctions on Russian diesel exports until 7 April.

Zelensky reacted by saying the relaxation of the penalties will allow Moscow to raise new funds to source new military equipment to continue the war.

He also accused Moscow of taking the deal "to mean they can keep fighting, to mean they keep dropping bombs on cities" following deadly new strikes on Zaporizhzhia.

On Saturday the EU's foreign affairs chief Kaja Kallas echoed Zelensky's criticism, saying suspending sanctions "provides Moscow with more revenues to wage war", adding: "This is not the time to ease pressure on Russia, and Europe won't."

She said European foreign ministers intended to approve the biggest set of sanctions on Russia since the start of its full-scale invasion on Monday.

The deal with Russia is the latest effort from Trump to lower fuel prices in the US ahead of the midterm elections, after months spent grappling with the political consequences of the Iran war.

That conflict, which began in February, has sent the cost of petrol and in particular diesel skyrocketing, which has soured his standing with the American public who have been stung by the higher pump prices and knock-on effects that led to across-the-board inflation.