Saudi Arabia said on Sunday it would retaliate to possible economic sanctions taken by other states over the case of Jamal Khashoggi, the state news agency SPA reported quoting an official source.

The kingdom will respond to any measure against it with bigger measures, the source said, adding: "The Saudi economy has vital and influential roles for the global economy."

"The Kingdom affirms its total rejection of any threats and attempts to undermine it, whether by threatening to impose economic sanctions, using political pressures, or repeating false accusations..." the official Saudi Press Agency quoted an unnamed government source as saying.

"The Kingdom also affirms that if it receives any action, it will respond with greater action, and that the Kingdom's economy has an influential and vital role in the global economy..." the source added without elaborating.

Saudi Arabia has been under pressure since Jamal Khashoggi, a prominent critic of Riyadh and a U.S. resident, disappeared on October 2 after visiting the Saudi consulate in Istanbul.

Read more: Saudi Stock Market Plummets After Trump Threatens 'Severe Punishment' Over Missing Journalist ■ 'Fake News' From Qatar or a Sign of MBS's Brutal Rule: Saudi Arabia Roiled by 'Murder' of Journalist

Twenty-two U.S. senators last Wednesday forced a U.S. investigation of whether human rights sanctions should be imposed over the disappearance of Khashoggi.

In a letter, the senators said they had triggered a provision of the Global Magnitsky Human Rights Accountability Act requiring the president to determine whether a foreign person is responsible for a gross human rights violation.

The Global Magnitsky Act requires a report within 120 days of the letter with a decision on the imposition of sanctions on anyone deemed responsible for a serious rights violation such as torture, prolonged detention without trial or extrajudicial killing of someone exercising freedom of expression.

>>'Murder' of Saudi dissident: Why Turkey is in no hurry to cut off ties with Riyadh

Trump vows "severe punishment" if it's confirmed Saudi Arabia behind disappearance of journalist Credit: 60 Minutes

U.S. President Donald Trump said in a CBS interview on Saturday that there would be "severe punishment" for Saudi Arabia if it turns out that missing Saudi journalist Khashoggi was killed in the Saudi consulate in Istanbul.

Asked whether Saudi Crown Prince Mohammed bin Salman gave an order to kill him, Trump said "nobody knows yet, but we'll probably be able to find out." Trump added in excerpts of the "60 Minutes" interview that will air on Sunday "we would be very upset and angry if that were the case".

"We're going to get to the bottom of it and there will be severe punishment," Trump said.

Trump has not described what punishment Saudi Arabia might face. He has indicated Washington does not want to harm close defence ties, saying the United States would be punishing itself if it halted sales of military equipment to Riyadh.

The threat caused the stock market of the world's biggest oil exporter to lose as much as $33 billion of its value on Sunday in one of the first signs of the economic pain that Riyadh could suffer over the affair.

The Saudi equities index plunged as much as 7 percent in its biggest drop since December 2014, when oil prices were crashing. It later recovered partially to stand 5.0 percent lower shortly before the close.

Turkey believes Khashoggi was deliberately killed in the consulate and his body removed. Riyadh has rejected those claims.

A senior member of Saudi Arabia's ruling family, Prince Khaled al-Faisal, has met Turkey's President Tayyip Erdogan to discuss Khashoggi's disappearance, two sources with knowledge of the matter told Reuters without providing details of the talks.

On Friday, a source with links to the prince's family said Prince Khaled, who is the governor of Mecca, had been sent to Turkey in his capacity as special adviser to King Salman.

INVESTMENT CONFERENCE

Foreign capital is key to Saudi Arabia's plans to diversify its economy beyond oil and cut a 12.9 percent jobless rate among its citizens.

But in response to Khashoggi's disappearance, media firms and some technology executives have pulled out of a major Riyadh investment conference scheduled for next week.

"This is happening at a time when Saudi Arabia is preparing for a big investment event and they don’t need people suspending or pulling out investments," said Nadi Barghouti, head of asset management at Emirates Investment Bank in Dubai.

U.S. Treasury Secretary Steven Mnuchin and Wall Street bankers will show up at an elite Saudi investment conference this month despite a growing exodus of top media companies and business leaders after the disappearance of a Saudi journalist.

Mnuchin's plan to attend the high-profile Future Investment Initiative conference in Riyadh follows U.S. President Donald Trump's comments that he saw no reason to block SaudiArabian investments in the United States despite concern over the welfare of Jamal Khashoggi.

"I am planning on going at this point. If more information comes out and changes, we can look at that, but I am planning on going," Mnuchin said in an interview with CNBC on Friday.

CNN, the Financial Times, the New York Times, CNBC and Bloomberg, as well as reporters and editors from the Economist, said they were no longer participating in the conference, which relies heavily on journalists to moderate top sessions.

CNBC and Bloomberg, along with Fox Business Network, were among media partners with a big role at the event, which begins on Oct. 23.

GLOBAL REACTION

French President Emmanuel Macron on Friday became the latest ally to demand answers from Saudi Arabia on the fate of veteran Saudi journalist Jamal Khashoggi, last seen in the Saudi consulate in Istanbul more than a week ago.

France had so far been guarded in its reaction to the disappearance; Paris and Riyadh enjoy close diplomatic ties and commercial relations spanning energy, finance and arms.

"I'm waiting for the truth and complete clarity to be established ", Macron said in an interview with France 24 television.

British billionaire Richard Branson said on Thursday that his Virgin Group would suspend its discussions with Saudi Arabia's Public Investment Fund over a planned $1 billion investment in the group's space ventures.

Former British Prime Minister Tony Blair said on Thursday that the disappearance of journalist Jamal Khashoggi was extremely troubling and went against the spirit of the reforms advocated by Saudi Crown Prince Mohammed bin Salman.

Britain's main opposition Labour Party added that it would stop selling arms to Saudi Arabia if it was in government, its foreign policy spokeswoman said on Sunday.