RIYADH - US top diplomat Mike Pompeo met Tuesday with Saudi King Salman and the crown prince seeking to defuse a crisis over missing journalist Jamal Khashoggi, with American officials saying Riyadh had agreed the need for a “thorough” probe.

The urgent talks came after US President Donald Trump dispatched Pompeo to the Gulf kingdom amid a growing international outcry about Khashoggi’s disappearance.

Khashoggi has not been seen since he walked into the Saudi consulate in Istanbul on October 2 to sort out marriage paperwork. “Rogue killers” could be to blame, Trump said after telephone talks on Monday with the king.

After first meeting with the king, Pompeo held separate talks with Minister of Foreign Affairs Adel al-Jubeir and powerful Crown Prince Mohammed bin Salman.

“We are strong and old allies. We face our challenges together,” the crown prince said as he warmly welcomed Pompeo at the palace. The two men were also due to have dinner together later Tuesday. “The secretary and the foreign minister agreed on the importance of a thorough, transparent, and timely investigation,” State Department spokeswoman Heather Nauert said later.

Turkish police Monday searched the consulate for the first time since the disappearance of Khashoggi, a Saudi national and US resident who had become increasingly critical of Prince Mohammed.

Turkish officials have said they believe he was killed - a claim Saudi Arabia has denied - with the controversy dealing a huge blow to the prince’s efforts to showcase a reform drive and burnish the kingdom’s image.

US President Donald Trump said Tuesday he had spoken with Saudi Crown Prince Mohammed bin Salman and been assured that a “full” probe into the disappearance of a critical journalist was underway.

“Just spoke with the Crown Prince of Saudi Arabia who totally denied any knowledge of what took place in their Turkish Consulate,” Trump tweeted.

He “told me that he has already started, and will rapidly expand, a full and complete investigation into this matter. Answers will be forthcoming shortly.”

Meanwhile, an influential US Senate ally of President Donald Trump pledged Tuesday that Congress would take decisive action against Saudi Arabia over a missing writer, calling for the ouster of Crown Prince Mohammed bin Salman.

“This guy is a wrecking ball. He had this guy murdered in a consulate in Turkey,” Republican Senator Lindsey Graham told “Fox and Friends,” one of the president’s favorite news broadcasts.

Graham, discussing the feared killing of Saudi journalist and US resident Jamal Khashoggi, a critic of the monarchy, was backed by Marco Rubio, another of the top Republicans in the upper house, who described the crown prince as “young and aggressive.”

But Graham, who has recently ingratiated himself with Trump, launched a tirade against Riyadh.

“I was on the (Senate) floor every time defending Saudi Arabia because they’re a good ally,” Graham told Fox.

“There is a difference between a country and an individual,” he added. “The MBS figure is to me toxic. He can never be a world leader on the world stage.”

Graham added that he felt “personally offended” by the kingdom’s leadership.

“They have nothing but contempt for us. Why would you put a guy like me and the president in this box after all the president has done?” Graham fumed. “This guy has got to go.”

US media reported on Monday that the oil-rich kingdom is considering an admission that Khashoggi died after an interrogation that went wrong during an intended abduction. The UN human rights chief called Tuesday for the lifting of the immunity of officials who might be involved in Khashoggi’s disappearance.

Due to the seriousness of the case “I believe the inviolability or immunity of the relevant premises and officials... should be waived immediately,” Michelle Bachelet said in a statement.

The investigators, who searched the premises for eight hours into Tuesday morning, took samples with them, including soil from the consulate garden, one official at the scene said. Istanbul police are now also planning to search the nearby consul’s residence, a diplomatic source said.

Trump’s comments came after a telephone conversation with King Salman, father of the crown prince, the first such talks since the crisis erupted.

“Just spoke to the King of Saudi Arabia who denies any knowledge of whatever may have happened ‘to our Saudi Arabian citizen’,” Trump tweeted.

“The denial was very, very strong,” Trump told reporters. “It sounded to me like maybe these could have been rogue killers. Who knows?”

But CNN cited two sources as saying the Saudis are preparing a report that his death resulted from a botched interrogation, while the Wall Street Journal said the kingdom was weighing whether to say that rogue operatives killed Khashoggi by mistake.

After his crunch talks in Riyadh Tuesday, Pompeo was expected in Turkey on Wednesday to meet Turkish Foreign Minister Mevlut Cavusoglu, the state-run Anadolu news agency said.

The controversy has troubled Saudi’s traditional Western allies, who are key arms suppliers to the kingdom, and also undermined efforts by Mohammed bin Salman to present himself as a modernising ruler.

An investment conference seen as a platform for the crown prince and dubbed the “Davos in the Desert”, scheduled to take place in Riyadh next week, has been hit by a string of prominent cancellations.

JPMorgan Chase CEO Jamie Dimon, Ford chairman Bill Ford and Larry Fink, the head of investment giant BlackRock, were among the latest business barons to cancel plans to attend.

US Treasury Secretary Steven Mnuchin said he still plans to attend but would “take (it)... into account” if more information came out.

The controversy meanwhile threw into doubt a $400 million deal the Saudi Public Investment Fund negotiated with Hollywood’s most powerful talent agency as part of the crown prince’s drive for a foothold in the entertainment industry.

Endeavor CEO Ari Emanuel said the Khashoggi case was “very, very concerning”, although he stopped short of pronouncing the deal was dead.

Trump has threatened the kingdom with “severe punishment” if it is shown that Khashoggi was killed inside its Istanbul mission.

But he has also made clear he is reluctant to curb all-important arms sales to Saudi Arabia.

Britain, France and Germany also released a rare joint statement saying they were treating Khashoggi’s disappearance “with the utmost seriousness” and calling for a “credible investigation”.X