Two key US Republican senators have said they have "zero" doubt Saudi Arabia's crown prince directed the murder of journalist Jamal Khashoggi.

CIA director Gina Haspel briefed a small group of senators today.

The new declarations by members of President Donald Trump's party run counter to the White House narrative downplaying possible links between Crown Prince Mohammed bin Salman and the October killing of Mr Khashoggi at the kingdom's Istanbul consulate.

"I have zero question in my mind that the crown prince directed the murder and was kept appraised of the situation all the way through it," Senate Foreign Relations Committee chairman Bob Corker said.

"If Mohammed bin Salman were in front of a jury he'd be convicted in less than 30 minutes."

Fellow Republican Senator Lindsey Graham, who has urged Mr Trump to take a far tougher stance against Riyadh over the killing, also attended the hour-long briefing.

He minced no words afterwards, saying he believes the Crown Prince is "a wrecking ball" who is "complicit in the murder of Mr Khashoggi to the highest level possible."

"There's not a smoking gun but a smoking saw," Mr Graham added.

The veteran journalist was a strong critic of Prince Mohammed and had been resident in the United States, where he wrote about politics in Saudi Arabia and the Middle East for The Washington Post.

The New York Times, the Journal and the Washington Post and have all reported that the CIA has evidence Prince Mohammed exchanged 11 messages with his close aide Saud al-Qahtani, who allegedly oversaw the murder, just before and after it took place.

After reports that the CIA concluded that the crown prince ordered Mr Khashoggi's assassination Mr Trump issued a statement saying US-Saudi relations and oil market stability were too important to rock over the scandal.

Last week, under mounting pressure from lawmakers on both sides of the political aisle who wanted action against Riyadh, Secretary of State Mike Pompeo and Pentagon chief Jim Mattis held a closed-door all-senators briefing where they said there was no direct evidence linking the crown prince to the murder.

Today, Senator Graham brushed their assessment aside.

"You have to be willfully blind not to come to the conclusion that this was orchestrated and organized by people under command of Prince Mohammed bin Salman, and that he was intricately involved in the demise of Mr Khashoggi."

Mr Trump has declined to accept the conclusion saying there is no direct evidence of it.