Defense Secretary James Mattis said there is "no smoking gun" proving that Saudi Crown Prince Mohammad bin Salman was involved in the killing of journalist Jamal Khashoggi.

Mattis, along with Secretary of State Mike Pompeo, briefed senators Wednesday on the civil war in Yemen, during which they spoke about the importance of the United States-Saudi Arabia relationship and defended the Trump administration's response to Khashoggi's brutal murder.

Speaking to reporters after the briefing, Mattis said he has personally read all the intelligence reports and transcripts related to the killing, which took place October 2 at the Saudi consulate in Istanbul, Turkey.

"We have no smoking gun that the crown prince was involved, not the intelligence community or anyone else," Mattis said.

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The U.S. has imposed sanctions on 17 Saudis who were involved in Khashoggi’s murder, but a bipartisan group of senators -- including Lindsey Graham (R-S.C.) -- favor harsher sanctions against the Saudi royal family, specifically the crown prince.

On "The Daily Briefing" Wednesday, Sen. John Barrasso (R-Wy.) said it's hard to believe that bin Salman would not have known about a plot to murder a prominent critic of the royal family, but, as Mattis said, there is no "definite link."

"No matter which way you look at it, the values of the United States, I think, have to be clearly stated. And we find that kind of activity -- what happened in Turkey to the reporter from the Washington Post -- is against every one of our values," Barrasso said.

The CIA previously concluded bin Salman ordered the murder of Khashoggi. 

Watch Mattis' remarks and the "Daily Briefing" interview above.

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