US Secretary of State Mike Pompeo says there is no direct evidence connecting Saudi Crown Prince Mohammed bin Salman to the murder of journalist Jamal Khashoggi last month in Istanbul.

Mr Pompeo spoke to reporters on Wednesday after he and Defence Secretary Jim Mattis told the Senate behind closed doors that weakening US-Saudi ties over the killing would hurt national security.

“There is no direct reporting connecting the crown prince to the order to murder Jamal Khashoggi,” Mr Pompeo said.

However, many senators left the briefing saying otherwise.

“I don’t think there’s anybody in the room that doesn’t believe he was responsible for it,” Senator Bob Corker, the Republican chairman of the Senate foreign relations committee, told reporters after the briefing.

“MbS (Mohammed bin Salman) has not taken ownership of the death,” Mr Corker said, using the short-hand initials for the Crown Prince.

The CIA has assessed that the crown prince had ordered the October 2 killing of Mr Khashoggi at the Saudi consulate in Istanbul.

Republican senator Lindsey Graham said he would withhold his vote on any key issue, including a government spending bill, until he gets a briefing on the topic from the CIA.

“I am not going to be denied the ability to be briefed by the CIA, that we have oversight of, about whether or not their assessment supports my belief that this could not have happened without MbS knowing,” Mr Graham told reporters.

Leading Democratic senators said the intelligence they had seen convinced them of the Crown Prince’s role in murder of Mr Khashoggi, a Washington Post journalist and US resident.

US President Donald Trump has vowed to remain a “steadfast partner” of Saudi Arabia and says it is not yet clear if the Crown Prince had been involved in the killing.