Russian President Vladimir Putin told U.S. President Donald Trump in a phone call on Thursday that Moscow wants a negotiated end to the Ukraine war but will not step back from its original goals, a Kremlin aide said.

In a wide-ranging conversation that also covered Iran and the Middle East, Trump "again raised the issue of an early end to military action" in Ukraine, the aide, Yuri Ushakov, told reporters.

"Vladimir Putin, for his part, noted that we continue to seek a political and negotiated solution to the conflict," Ushakov said.

Putin briefed Trump on the implementation of agreements reached between Russia and Ukraine last month to exchange prisoners-of-war and dead soldiers, Ushakov said, and told him that Moscow was ready to continue negotiations with Kyiv.

"Our president also said that Russia will achieve the goals it has set: that is, the elimination of the well-known root causes that led to the current state of affairs, to the current acute confrontation, and Russia will not back down from these goals," he added.

There was nothing in the Kremlin readout to suggest that Putin had made any shift in Moscow's position during the conversation with Trump, who took office with a promise to end the war swiftly but has voiced frequent frustration with the lack of progress between the two sides.

The phrase "root causes" is shorthand for the Kremlin's argument that it was compelled to go to war in Ukraine to prevent the country from joining NATO and being used by the Western alliance as a launch pad to attack Russia.

Ukraine and its European allies say that is a specious pretext for what they call an imperial-style war, but Trump in previous public comments has shown sympathy with Moscow's refusal to accept NATO membership for Ukraine.

Putin and Trump did not talk about the U.S. decision to halt some shipments of critical weapons to Ukraine, Ushakov said.

On Iran, he said, "the Russian side emphasised the importance of resolving all disputes, disagreements and conflict situations exclusively by political and diplomatic means".

Trump last month sent U.S. military bombers to strike three Iranian nuclear sites, in a move condemned by Moscow as unprovoked and illegal.