Lindsey Graham
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Senator Lindsey Graham
U.S. Senator Lindsey Graham has made a veiled criticism of Saudi Crown Prince Mohammed bin Salman.

After he met with Turkish President Recep Tayyip Erdogan, Graham said in Ankara on Saturday that the U.S. Congress will reintroduce sanctions against those implicated in the brutal murder of Washington Post journalist Jamal Khashoggi.

Riyadh says the crown prince did not know about the killing in the Saudi consulate in Istanbul in October, claims that have been cast into doubt by Riyadh's contradictory explanations.

The CIA concluded in November that the prince ordered the journalist's assassination, which Riyadh denies.

Although President Donald Trump has been reluctant to criticize the prince, Graham said on Saturday: "The relationship between the U.S. and Saudi Arabia cannot move forward until Crown Prince Mohammed bin Salman is dealt with," without specifying what this meant, Reuters reported.

Washington sanctioned 17 Saudi officials in November for their alleged role in the Khashoggi killing. Ties have also been strained by the Senate's vote to push for ending military support for the Saudi-led coalition in the war in Yemen.

Graham, who is on the Senate's Armed Services Committee, also said he hoped Trump would slow the U.S. withdrawal from Syria until the Islamic State militant group (Isis) is destroyed.

On Wednesday, Graham expressed concern that Trump's statements about Syria have emboldened Isis. "My concern, by the statements made by President Trump, is that you set in motion enthusiasm by the enemy we're fighting.

"You make people we're trying to help wonder about us. And as they get bolder, the people we're trying to help are going to get more uncertain. I saw this in Iraq. And I'm now seeing it in Syria," he said, according to CNN.

Graham also said in Ankara that by arming the YPG group in Syria, Washington had "created a nightmare for Turkey."

He said that Washington would work with Turkey to move Kurdish YPG elements away from the country.