US President Donald Trump has urged Turkey to stop buying oil from Russia, part of a wider drive to cut off Moscow's energy funding as the war in Ukraine rages on.

Speaking alongside Turkish President Recep Tayyip Erdogan at the White House, Trump said halting those imports would be 'the best thing' his Turkish counterpart could do.

The Oval Office meeting ended without any firm commitments to lift US sanctions on Turkey or to sell advanced F-35 fighter jets, though Trump expressed optimism on both issues.

Turkey has for years been prevented from buying US F-35s. In 2019, it was expelled from a programme where it produced parts for the warplane after it acquired air defence systems from Russia.

During a brief question-and-answer session alongside Erdogan in the Oval Office on Thursday, Trump said he would like Turkey to stop 'buying any oil from Russia while Russia continues its rampage against Ukraine'.

'The best thing he could do is not buy oil and gas from Russia,' Trump said. 'If he did that, that would be the best thing.'

Trump added that he believes Erdogan is respected both by Ukrainian President Volodomyr Zelensky and Russian President Vladimir Putin, meaning that he could 'have a big influence' on the war 'if he wants to'.

Alongside India and China, Turkey is among Moscow's biggest customers for oil and gas exports, and data shows that the volume of Russian gas that reached Europe through Turkey rose by more than 26% earlier this year.

The US president's comments come just weeks after he said he stood poised to impose tougher sanctions on Russia if NATO countries met conditions that included halting imports of Russian oil.

Earlier this week - during a lengthy speech at the UN General Assembly - Trump also accused NATO allies of 'funding the war against themselves' through their purchases of energy from Moscow.

During Trump's first term in office, the US removed Turkey from the F-35 programme after it purchased S-400 surface-to-air missile systems from Russia.

A US defense bill passed in 2020 included an amendment that prevented Turkey from acquiring F-35s, unless the US government was able to certify that it had given up on the Russian S-400.

Some US lawmakers have expressed concerns about the potential sale over Turkish military incursions into Syria and past violations of Greek airspace.

Trump also said that sanctions against Turkey - implemented in 2020 following the S-400 purchase - could be lifted 'very soon'.

'If we have a good meeting, almost immediately,' he added.