US President Donald Trump has accused Saudi authorities of staging the “worst cover-up ever” in the killing of prominent journalist Jamal Khashoggi.

Asked by a reporter in the White House Oval Office on Wednesday morning (AEST) how the Washington Post columnist’s killing could have happened, Mr Trump replied: “They had a very bad original concept”.

“It was carried out poorly, and the cover-up was one of the worst in the history of cover-ups,” he said.

Mr Khashoggi’s death in the Saudi consulate in Istanbul on October 2 has caused global outrage and strained relations between Riyadh and Washington.

A vocal critic of Saudi Crown Prince Mohammed bin Salman, Mr Khashoggi was a US resident.

Mr Trump’s latest comments on the incident are in contrast to those the President has made in recent days, which have ranged from threatening Saudi Arabia with “very severe” consequences to more conciliatory remarks highlighting the country’s role as a US ally against Iran and Islamist militants, as well as a major purchaser of US arms.

Mr Trump on Wednesday said the Khashoggi matter was handled badly by Saudi officials.

“Bad deal. Should have never been thought of. Somebody really messed up. And they had the worst cover-up ever,” Mr Trump said.

While Mr Trump is yet to give his view on who was ultimately responsible for the killing, Secretary of State Mike Pompeo says some Saudi government and security officials have been identified and appropriate actions will be taken against them, including revoking their visas.

“These penalties will not be the last word on the matter from the United States,” Mr Pompeo told reporters on Wednesday morning.

“We’re making very clear that the United States does not tolerate this kind of ruthless action to silence Mr Khashoggi, a journalist, through violence.”

Riyadh initially denied knowledge of Mr Khashoggi’s fate before saying he was killed in a fight in the consulate, a reaction that has met with skepticism from several Western governments, straining their relations with the world’s biggest oil exporter.

The kingdom has since changed parts of its official narrative about the killing, further deepening international concern.

Turkish President Recep Tayyip Erdogan earlier laid out the Saudi planning of Mr Khashoggi’s “premeditated murder”, demanding that the suspects face justice in Turkey amid reports the journalist’s remains have been found.

Mr Erdogan, in his first extended remarks on the case, outlined the chronology of the murder and offered some new details.

Mr Erdogan made it clear the investigation was not over. Photo: AP

The Turkish President dismissed attempts by Riyadh to blame the “savage” killing on rogue operatives, but did not mention Saudi Crown Prince Mohammed bin Salman, who some US politicians suspect ordered the killing.

The impassioned speech came shortly before media reports claimed that body parts were discovered in the gardens of the Saudi consul general in Istanbul.

Citing legal and political sources, Sky News reported that Mr Khashoggi’s body was “cut up” and his face “disfigured”.

One source was quoted as saying Mr Khashoggi’s remains were discovered in the garden of the Saudi consul general’s home around 500 metres from the consulate, where he was last seen on October 2.

Turkish officials suspect Mr Khashoggi was killed and dismembered inside the consulate by Saudi agents.

Turkish sources have told media outlets that investigators have an audio recording purportedly documenting the killing.

Mr Erdogan made no reference to any audio recording in his speech, but made clear he had no intention of dropping the case, saying Turkey would not complete its investigation into Mr Khashoggi’s death until all questions were answered.

“Intelligence and security institutions have evidence showing the murder was planned…. Pinning such a case on some security and intelligence members will not satisfy us or the international community,” the Turkish President said.

– with AAP