Kyiv, Ukraine - Kyiv and Washington are engaged in talks over a deal to hand the US preferential access to Ukraine's mineral deposits, a source in Kyiv said on Friday – despite a dramatic spat between leaders Volodymyr Zelensky and Donald Trump.

The US president's top advisers have doubled down on their attacks on the Ukrainian leader in recent days, after Trump branded him a "dictator" and said Ukraine had "started" the war with Russia.

The war of words has stunned Kyiv and European capitals, a sign of just how rapidly Trump is overhauling Washington's long-standing support for Ukraine as he opens talks with Moscow on a settlement to the conflict.

The US had been Ukraine's most important financial, military, and political backer since Russia invaded in February 2022, in what the West's top powers had condemned as an unprovoked and illegal war of aggression.

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Despite the tensions between Zelensky and Trump, talks on a possible agreement to give the US preferential access to Ukraine's critical resources and minerals were "ongoing" on Friday, a senior Ukrainian official with knowledge of the matter told AFP.

Kyiv had rejected a first attempt by Trump's team to strike a deal for Ukraine's natural resources, saying the proposal did not include security guarantees for Kyiv – a move that infuriated Trump.

"There is a constant exchange of drafts, we sent another one yesterday," the Kyiv source said, adding that Ukraine was now waiting for a US response.

Trump's National Security Advisor Mike Waltz on Thursday publicly told Kyiv to "take a hard look and sign that deal."

"President Trump is obviously very frustrated right now with President Zelensky, the fact that he hasn't come to the table, that he hasn't been willing to take this opportunity that we have offered," he said.

Trump wants Ukraine to give US companies access as compensation for tens of billions of dollars of aid delivered under his predecessor Joe Biden.

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But Ukraine is seeking security guarantees from the US in exchange for signing away precious rights to vast amounts of its natural resources and critical minerals.

It is pressing for NATO membership or for the deployment of Western troops and masses of advanced equipment as part of any wider ceasefire agreement with Russia.

Zelensky said earlier this week he would not "sell" Ukraine in any deal with the US.

The spat risks undermining Western support for Kyiv at a critical juncture in the conflict, ahead of the three-year anniversary of Russia's invasion on Sunday.

Russia's army on Friday said it had captured two more villages in eastern Ukraine.