As the Riyadh stock market plunged on growing investor jitters, Saudi Arabia warned Sunday that it would retaliate against any sanctions imposed on the oil-rich kingdom over the disappearance of journalist Jamal Khashoggi, AFP reported.

Khashoggi, a Washington Post contributor, vanished after entering the kingdom’s Istanbul mission on October 2.

A growing number of Western companies are now distancing themselves from the Gulf state, potentially putting Crown Prince Mohammed bin Salman’s much-vaunted economic reform campaign in jeopardy.

US President Donald Trump threatened ally Saudi Arabia on Saturday with “severe punishment” if Khashoggi, who has been critical of Prince Mohammed, was murdered inside its Istanbul embassy.

But Riyadh vowed to retaliate against any punitive measures.

“The kingdom affirms its total rejection of any threats or attempts to undermine it, whether through threats to impose economic sanctions or the use of political pressure,” said an official source quoted by state news agency SPA.

The source added that Riyadh would “respond to any action with a bigger one,” pointing out that the oil superpower “plays an effective and vital role in the world economy.”

According to Saudi-owned Al Arabiya television, Riyadh has “over 30 measures” that it could wheel out to retaliate against sanctions. They include using the sales of oil and arms, the exchange of intelligence between Riyadh and Washington, and a possible reconciliation with regional arch-rival Iran, said the TV report.

Following Riyadh’s threat to retaliate against sanctions, Britain, France and Germany released a joint statement saying they were treating Khashoggi’s disappearance “with the utmost seriousness.”

“There needs to be a credible investigation to establish the truth about what happened, and – if relevant – to identify those bearing responsibility for the disappearance of Jamal Khashoggi, and ensure that they are held to account.”

Meanwhile, Turkish President Recep Tayyip Erdogan and Saudi King Salman on Sunday discussed the Khashoggi case in their first telephone conversation about the matter, AFP reported.

Erdogan and Salman discussed “the issue of shedding light on the case of Jamal Khashoggi” and also stressed the “importance of creating a joint working group within the framework of the investigation,” said an anonymous Turkish presidential source.

The king phoned Erdogan “to thank the president for welcoming the kingdom’s proposal to form a joint working group to discuss the disappearance of Saudi citizen Jamal Khashoggi.”

The Saudi foreign ministry said Salman affirmed his country’s “solid” relations with Turkey in the call with Erdogan.