The Trump administration has said it has not reached a final conclusion on who was involved in the death of the Saudi journalist, Jamal Khashoggi.

Speaking in California, US President Donald Trump said that the killing "should never have happened".

He said he would receive a report on Tuesday on who the US government believed killed Mr Khashoggi and what the overall impact of his murder is.

Mr Trump made the remarks hours after the State Department said the government was still working on determining responsibility for the death, and despite a CIA assessment that Saudi Crown Prince Mohammed bin Salman ordered the killing.

In a statement, State Department spokeswoman Heather Nauert said: "Recent reports indicating that the US government has made a final conclusion are inaccurate".

"There remain numerous unanswered questions with respect to the murder of Mr.Khashoggi."

She said the State Department will continue to seek facts and work with other countries to hold those involved in the journalist's killing accountable "while maintaining the important strategic relationship between the United States and Saudi Arabia".

White House spokeswoman Sarah Huckabee Sanders told reporters that Mr Trump discussed the CIA assessment by phone with the agency's director, Gina Haspel, and Secretary of State, Mike Pompeo, while flying to California on Saturday.

On Friday, sources told the Reuters news agency that the CIA had briefed other parts of the US government including Congress, on its assessment, a development that complicates President Trump's efforts to preserve ties with Saudi Arabia, a key US ally.

A source familiar with the CIA's assessment said it was based largely on circumstantial evidence relating to the prince's central role in running the Saudi government.

The CIA's finding is the most definitive US assessment to date tying Saudi Arabia's de facto ruler directly to the killing and contradicts Saudi government assertions that Prince Mohammed was not involved.

Mr Khashoggi, a critic of the crown prince, was killed in October at the Saudi consulate in Istanbul in Turkey when he went there to pick up documents he needed for his planned marriage.

As politicians push legislation to punish Saudi Arabia for the killing, both Republican and Democratic senators yesterday urged Mr Trump to be tough on the crown prince, with who he has cultivated a deep personal relationship.

Senator Bob Corker, chairman of the Senate Foreign Relations Committee, Tweeted: "Everything points to the Crown Prince of Saudi Arabia, MbS,ordering @washingtonpost journalist Jamal #Khashoggi's killing.

"The Trump administration should make a credible determination of responsibility before MbS executes the men who apparently carried out his orders".

President Trump and his senior officials have said Saudi Arabia should be held to account for any involvement in Mr Khashoggi's death and have imposed sanctions on 17 Saudis for their role in the killing.

They have also stressed the importance of Washington's ties with Riyadh, one of the biggest clients of the US defence industry.

Mr Trump wants to preserve the Saudi arms deals, despite growing opposition in Congress, saying: "They have been a truly spectacular ally in terms of jobs and economic development.  As president, I have to take a lot of things into consideration."

Marine General Joseph Dunford, chairman of the Joint Chiefs of Staff, noted yesterday that the kingdom plays a key military role for the United States in the Middle East.

He told a security forum in Halifax, Nova Scotia, in Canada,"Saudi Arabia has been an important partner to regional security in the past, I expect they will be in the future," adding that Middle Eastern allies including Saudi Arabia are "a stabilising force" in the region.

On Thursday, Saudi Arabia's public prosecutor said he was seeking the death penalty for five suspects charged in Mr Khashoggi’s killing.

The prosecutor, Shaalan al-Shaalan, told reporters the crown prince knew nothing of the operation, in which the journalist’s body was dismembered and removed from the consulate.

Saudi officials have said a team of 15 Saudi nationals were sent to confront Mr Khashoggi and he was accidentally killed in a chokehold by men who were trying to force him to return to the kingdom.

Politicians critical of Saudi Arabia for Mr Khashoggi's killing and its role in Yemen's civil war are ramping up their efforts to clamp down on the country.

Democratic Senator, Richard Blumenthal, Tweeted: "Trump  must accept (for once) his intelligence experts incontrovertible conclusion: Crown Prince MBS is culpable for Khashoggi’s monstrous murder. This brazen killing must have consequences, sanctions, prosecution, removal of MBS & others, not continued cover-up, enabled by Trump."