Riyadh Saturday dismissed Ankara's calls to extradite 18 Saudis being held over the murder of critic Jamal Khashoggi, as Washington warned the crisis risked destabilising the Middle East.

"The individuals are Saudi nationals. They're detained in Saudi Arabia, and the investigation is in Saudi Arabia, and they will be prosecuted in Saudi Arabia," Foreign Minister Adel al-Jubeir told a regional defence forum in Bahrain.

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He was responding to Turkish President Recep Tayyip Erdogan who on Friday renewed his call for the 18 men to be extradited for trial in Turkey.

Saudi journalist Khashoggi, 59, who had lived in self-imposed exile in the United States since 2017, was murdered after entering his country's Istanbul consulate on October 2 to obtain paperwork to marry his Turkish fiancee.

Gruesome reports have alleged that he was killed and dismembered by a team sent from Saudi Arabia to silence the Washington Post columnist, who had criticised the kingdom's powerful Crown Prince Mohammed bin Salman.

After weeks of denials, Riyadh has sought to draw a line under the crisis with an investigation.

Prince Mohammed, heir to the oil-rich nation's throne, publicly denounced the murder as "repulsive", while the Saudi prosecutor acknowledged for the first time this week that based on the evidence of a Turkish investigation the killing had been "premeditated".

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'Coordinated response'

But US Defence Secretary Jim Mattis, who was also addressing the Manama forum, warned that "the murder of Jamal Khashoggi in a diplomatic facility must concern us all greatly".

"Failure of any nation to adhere to international norms and the rule of law undermines regional stability at a time when it is needed most," he stressed.

The journalist's murder has generated international outrage and undermined Riyadh's relations with the United States and other Western governments.

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France and Germany's leaders said Saturday they want a "coordinated" European position for sanctions on arms sales to Saudi Arabia.

This came after French President Emmanuel Macron had on Friday implied German Chancellor Angela Merkel's government was engaging in "pure demagoguery" by halting arms sales to Riyadh.

On the sidelines of a Syria summit in Istanbul, the two leaders had a "peaceful exchange", the Elysee palace said, and agreed not to announce their next positions on the issue without first coordinating "at the European level".

The Saudi foreign minister vowed Saturday that the kingdom would "overcome" the crisis over Khashoggi's killing.

"The issue, as I said, is being investigated. We will know the truth. We will hold those responsible accountable. And we will put in place mechanisms to ensure it doesn't happen again," Jubeir told the defence forum.

Beyond the detention of the 18 suspects, five Saudi intelligence chiefs have been sacked, including two who were part of the crown prince's inner circle.

On Thursday, CIA Director Gina Haspel briefed US President Donald Trump on the latest developments in the investigation after a fact-finding mission to Turkey.

Pro-government Turkish media said intelligence officers showed Haspel video images and audio tapes of Khashoggi's killing gathered from the consulate.

Once an insider in Saudi royal circles, Khashoggi fell out of favour with the monarchy after Mohammed bin Salman was named heir to the throne last year.

The columnist went into self-imposed exile in the United States, where he wrote a column for The Washington Post, which was often critical of the crown prince.

Khashoggi was least seen entering the Saudi consulate in Istanbul on October 2 to complete paperwork for his wedding to his Turkish fiancee, Hatice Cengiz.

She has demanded punishment of everyone involved in his murder "from the highest to the lowest levels."