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Relations between the United States and Saudi Arabia cannot progress until Crown Prince Mohammed bin Salman is "dealt with," Sen. Lindsey Graham said on Saturday during a visit to Turkey.

The South Carolina Republican has become a fierce critic of the kingdom's de facto ruler since the murder of journalist Jamal Khashoggi in October. Graham's latest comments come as tensions in the region run high amid U.S. plans to withdraw troops from Syria.

"What has transpired over the [last] couple of years has been unnerving to say the least," Graham said about the crown prince's leadership. "Taking all of your critics and throwing them in prison, the brutal murder [of] Mr. Khashoggi in Turkey, violating every norm of international behavior."

Khashoggi, a Washington Post columnist and critic of Prince Mohammed, was killed by a team sent from Riyadh after he entered the Saudi Consulate in Istanbul on Oct. 2. Saudi authorities have acknowledged that the killing was premeditated, but blamed it on rogue operatives. His body has not been found.

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Khashoggi's death triggered a wave of revulsion around the globe, and drew attention to Saudi Arabia's increasingly aggressive regional policies, like its involvement in the war in neighboring Yemen which has produced one of the world's worst humanitarian crises.

U.S. intelligence officials have told NBC News that it is inconceivable that the crown prince had no connection to Khashoggi's death. Graham himself has said there is "zero chance" the killing was organized without the prince's knowledge.

President Donald Trump has tried to downplay Prince Mohammed's role in the murder, and highlighted business deals with the kingdom and Saudi Arabia's role in containing Iran.

While Prince Mohammed was initially hailed for spearheading huge changes in the conservative kingdom — moves aimed at lessening its dependence on oil, loosening the conservative clerical class's grip on power and forcing social changes — his widening crackdown on dissent has eclipsed the positive PR the reforms brought.

On Friday, Graham had met with Turkish President Tayyip Erdogan, who has reacted angrily to Khashoggi's killing in Istanbul. The senator vowed that Congress would reintroduce sanctions against those involved in the incident on Turkish soil.

Graham was expected to discuss the U.S. withdrawal from Syria, which Trump announced on Dec. 19 in a sudden policy shift that blindsided Congress and most senior officials at the Pentagon and State Department.

Turkey considers Syrian Kurds, who are fighting Islamic State forces alongside Americans, to be terrorists. There are concerns that Turkey, a NATO member, will invade Syria in the absence of American forces.

National security adviser John Bolton has said that a withdrawal from the region will not happen until the Turkish government guarantees it won't attack America's allies.

Graham's visit was expected to include a proposal for the creation of a "safe zone" in northeast Syria.

ISIS killed two U.S. service members and two American civilians in the northeastern town of Manbij in a suicide bombing just days before the visit. Graham has said he's concerned Trump's withdrawal announcement has emboldened ISIS, endangering American allies.