US Secretary of State Mike Pompeo said Wednesday that there is no "direct information" connecting Saudi with the murder of journalist Jamal Khashoggi in Istanbul, and he warned that it would be a "grave mistake" to degrade US-Saudi relations because of the killing.

"There is no direct reporting connecting the crown prince to the order to murder Jamal Khashoggi," Pompeo said in remarks to reporters after holding a closed-door meeting with senators to inform them of US intelligence findings on the matter.

Pompeo said that degrading US-Saudi ties because of Khashoggi's murder would be a "grave mistake" for US "national security" after the meeting on Capitol Hill, in which Defense Secretary James Mattis also participated.

Several days ago President Donald Trump called Khashoggi's killing an "atrocity", but he said that the CIA had not reached a definitive "conclusion" about the crown prince's involvement in the murder last month at the Saudi consulate in Istanbul.

Khashoggi, as Riyadh has admitted, was murdered by a group of agents who traveled to Istanbul from Saudi Arabia -- some of them close associates of the crown prince. The journalist, who had been living in the US and writing periodic columns for The Washington Post, had gone to the Saudi consulate in Istanbul on October 2 to get documents he needed to marry his Turkish fiancee.

Meanwhile, Pompeo defended Washington's involvement in the conflict in Yemen, in which some 10,000 people have died and which has become the world's biggest humanitarian crisis at present.

The US has been backing the coalition headed by Saudi Arabia that is fighting the Houthis rebels, supported by Iran.

"The suffering in Yemen grieves me, but if the United States of America was not involved in Yemen, it would be a hell of a lot worse," said Pompeo in prepared remarks, adding that "abandoning Yemen would do immense damage to US national security interests and those of our Middle Eastern allies and partners".