Donald Trump says he is standing by Saudi Arabia's Crown Prince despite a CIA assessment Mohammed bin Salman ordered the killing of journalist Jamal Khashoggi, and as senators plea for the US President to condemn the kingdom's de facto ruler.

Key points: Mr Trump said that "at this moment" he supports Mohammed bin Salman

Mr Trump said that "at this moment" he supports Mohammed bin Salman MbS is reportedly facing a push from within the ruling family to stop him from becoming king

MbS is reportedly facing a push from within the ruling family to stop him from becoming king Mr Trump ruled out cutting Saudi Arabia's US weapons supply but said he is open to ending US support in Yemen

Speaking in an Oval Office meeting with Reuters, Mr Trump refused to comment on whether Mohammed bin Salman was complicit in the murder, but he provided perhaps his most explicit show of support for the Prince since Khashoggi's death more than two months ago.

"He's the leader of Saudi Arabia. They've been a very good ally," Mr Trump said in the interview.

Asked by Reuters if standing by the kingdom meant standing by the Prince, known as MbS, Mr Trump responded: "Well, at this moment, it certainly does."

Some members of Saudi Arabia's ruling family are agitating to prevent MbS from becoming king, sources close to the royal court have told Reuters, and believe the United States and Mr Trump could play a key determining role in who ultimately assumes the position.

"I just haven't heard that," Mr Trump said.

"Honestly, I can't comment on it because I had not heard that at all. In fact, if anything, I've heard that he's very strongly in power."

While Mr Trump has condemned the murder of Khashoggi — a US resident and Washington Post columnist who was often critical of MbS — he has given the benefit of the doubt to the Prince with whom he has cultivated a deep relationship.

Khashoggi was also named Time Magazine's person of the year, alongside a group of journalists who have fought as "guardians" in the war on truth.

Saudi journalist Jamal Khashoggi was killed at the Saudi Arabian consulate in Istanbul in October. ( Supplied: Time )

Mr Trump again reiterated the "Crown Prince vehemently denies" involvement in a killing that has sparked outrage around the world.

The US President has come under fierce criticism from fellow Republicans in the Senate over the issue, particularly after CIA director Gina Haspel briefed them with the agency's assessment MbS ordered the killing.

In response to the CIA's assessment, Mr Trump called the conclusion "very premature".

"You have to be wilfully blind not to come to the conclusion that this was orchestrated and organised by people under the command of MbS," Republican Senator Lindsey Graham, a Trump ally, said last week.

Senator Graham and other senators who have supported the US-Saudi alliance over the years have said Mr Trump should impose more sanctions after a first round targeted 17 Saudis for their alleged role in the killing in the Saudi consulate in Istanbul on October 2.

As the Senate this week considers a joint resolution condemning the Crown Prince for the killing — something the President would have to sign or veto if passed by Congress — Mr Trump said he would meet with senators.

Mr Trump said he hoped senators would not propose stopping arms sales to the Saudis, deals he has doggedly fought to save ever since the gruesome details of Khashoggi's murder were leaked by Turkey.

"And I really hope that people aren't going to suggest that we should not take hundreds of billions of dollars that they're going to siphon off to Russia and to China," Mr Trump said.

Mr Trump said he could abide by legislation ending US support for the Saudi-led war effort in Yemen, a proxy war with regional rival Iran that has led to a deepening humanitarian disaster.

"Well, I'm much more open to Yemen because frankly, I hate to see what's going on in Yemen," Mr Trump said.

"But it takes two to tango. I'd want to see Iran pull out of Yemen too … and I think they will."

Reuters