The Turkish leadership has so far stopped short of accusing Saudi Arabia, although pro-government media have published sensational claims, including that an "assassination team" was sent to Istanbul to kill Khashoggi.
"He is being outdone by Donald Trump, whoever would have thought that?" she said on BBC's The Andrew Marr Show.
Donald Trump: Africans Love Melania
Trump joins other first ladies - including Laura Bush, Hillary Clinton and Michelle Obama - in embarking on solo trips to Africa. Egypt will be her final stop on her tour of the continent that focuses on child welfare, education, tourism and conservation.
"There's not enough money in the world for us to buy back our credibility on human rights if we do not move forward and take swift action", Rubio said.
Saudi Arabia has said it had nothing to do with Mr Khashoggi's disappearance, without explaining or offering evidence of how the writer left the consulate and disappeared into Istanbul with his fiancee waiting outside.
Florida Republican Marco Rubio tells CNN's "State of the Union" that he doesn't think any USA government officials "should be going and pretending as it's business as usual, until we know exactly what's happened here".
The warning from Al Arabiya's Turki Aldakhil comes amid heightened tensions between Saudi Arabia and the West, after journalist Jamal Khashoggi - a USA resident and prominent critic of Crown Prince Mohammed bin Salman - disappeared after entering the Saudi consulate in Istanbul on October 2.
As you can imagine, more people are reading The Jerusalem Post than ever before. Kudlow isn't saying what Trump could do, but says Trump will "decide what the proper actions" are.
The Saudis themselves are warning they'll respond to any "threats" against the Kingdom.
The UK, France and Germany added to the pressure on Sunday, calling for a credible probe and urging Saudi Arabia to provide detailed answers.
'Stop And Frisk' Works, Chicago Should 'Strongly Consider' It
Trump and Rosenstein had been scheduled to meet last week to discuss The New York Times report that flung Rosenstein into limbo. As the plan was taking shape, Rosenstein went to the White House expecting he would be fired but wound up staying in his job.
USA lawmakers, for their part, have come out more strongly.
"If Khashoggi had disappeared in Turkey when he was at a hotel or a private residence, I think there is plausible deniability on the part of the Saudi government", Brennan told NBC's "Meet the Press."
Yemeni Nobel Peace Prize laureate Tawakkol Karman (center) joins a demonstration outside the Saudi consulate in Istanbul earlier earlier this month.
A joint statement of condemnation, if it is confirmed that Mr Khashoggi was killed by Saudi agents, is also being discussed by United States and European diplomats.
Describing the disappearance as a "terrible thing", Trump said the USA would find out what happened to Khashoggi.
US President Donald Trump said he would "punish" Saudi Arabia if it were found responsible for killing him.
The main stock market index in Riyadh fell as much as 7% on Sunday and billions of dollars were wiped off the value of leading Saudi companies.
Lawyer: FBI has completed Mark Judge interview
Opposition to Kavanaugh grew 4 percentage points after the hearing, apparently driven by people who previously were undecided. Trump initially was deferential to Ford, describing her late last week as a "very fine woman" and a "credible witness".
Report claims Mourinho will be sacked this weekend
Sources at United have told ESPN FC that they believe Mourinho to be increasingly unhappy and ill-tempered at the club. Last weekend's 3-1 loss at the London Stadium was United's third league defeat of the season.