WASHINGTON/ ISTANBUL - US President Donald Trump has accused Saudi Arabia of lying about the killing of Jamal Khashoggi, his strongest comments to date on the affair as pressure was building Sunday on the administration to strike a tougher line.

In an interview with the Washington Post published late Saturday, Trump stepped back from his stance that Saudi Arabia's latest explanation for the death of the journalist inside their Istanbul consulate was credible, but said he remained confident in the leadership of Crown Prince Mohammed bin Salman.

"Obviously there's been deception and there's been lies," he said of the shifting accounts offered by Riyadh.

Saudi officials originally said Khashoggi, who entered the diplomatic mission on October 2, had left unharmed, before announcing Friday he was killed inside the building in what they described as an altercation.

"Their stories are all over the place," added Trump.

Saudi Arabia faced a growing chorus of incredulity Sunday, with world powers demanding answers. British and French officials denounced the latest Saudi explanation as insufficient. Canada's foreign minister, Chrystia Freeland, said the Saudi version lacked "consistency and credibility."

Closer to home, pressure continued to grow on Trump to take a stronger stance against Saudi Arabia, the world's biggest oil exporter and a key regional power. Several senior members of Trump's Republican Party said they believed Prince Mohammed, the kingdom's de facto ruler, was linked to the killing, and one called for a "collective" Western response if a link is proved.

But Trump stopped far short of calling for the prince to be replaced, emphasizing as he has before how important the US-Saudi relationship is to Washington's regional strategic goals.

He described the 33-year-old prince, widely known as MBS, as a "strong person; he has very good control."

"He's seen as a person who can keep things under check," added Trump. "I mean that in a positive way."

Trump added that he has yet to be shown any evidence by intelligence officials that would make him believe MBS had any direct role.

"Nobody has told me he's responsible. Nobody has told me he's not responsible. We haven't reached that point. I haven't heard either way," the president said.

"There is a possibility he found out about it afterward. It could be something in the building went badly awry. It could be that's when he found out about it. He could have known they were bringing him back to Saudi Arabia." Amid Trump's apparent equivocations, several key Republicans demanded a tougher stance.

Meanwhile, Turkish President Recep Tayyip Erdogan on Sunday vowed to reveal within days the "naked truth" over the death of journalist Jamal Khashoggi as Riyadh insisted it did not know the whereabouts of his body and that Crown Prince Mohammed bin Salman had been unaware of any operation to kill him.

In his strongest comments to date on the affair, US President Donald Trump has accused Saudi Arabia of lying about the killing of Khashoggi, a Washington Post columnist who fell out of favour with Riyadh, as pressure built on the administration to strike a tougher line.

But the Saudi foreign minister, Adel al-Jubeir, insisted on Sunday that Prince Mohammed was "not aware" of the killing and that the kingdom does not know where the body is. Erdogan, whose ties to Saudi Arabia appear to have further soured over the Khashoggi case, said he would reveal the findings of his country's investigation into the killing in the coming days.

The Turkish leader's statement came the day after Saudi authorities conceded Khashoggi had been killed inside their diplomatic compound in Istanbul.

"We are looking for justice here and this will be revealed in all its naked truth, not through some ordinary steps but in all its naked truth," Erdogan told a rally in Istanbul.

Erdogan is expected to make a full statement to his party's MPs in parliament on Tuesday.

Turkish officials have said they believe that 15 Saudi men who arrived in Istanbul on two flights on October 2 were connected to his death.

Riyadh reacted by claiming one of the 15 had died in a car accident years ago.

Saudi officials originally said Khashoggi, who stepped inside the doors of the diplomatic mission on October 2, had left unharmed, before announcing he was killed inside the building in what they described as an altercation.

The kingdom has since admitted Khashoggi died in a "brawl" inside the consulate and said it has fired five top officials and arrested 18 others in an investigation into the killing.

"Why did the 15 men come here? Why were the 18 people arrested? That should be explained in all its details," said Erdogan.

Khashoggi, who would have been 60 this month, sought refuge in the United States after he fled his native Saudi Arabia following the 2017 appointment of strongman Mohammed bin Salman as heir to the throne.