US President Donald Trump said he believes missing journalist Jamal Khashoggi is probably dead, as a probe continues into the disappearance of the dissident writer.

"It certainly looks that way to me," Trump said Thursday when asked if Khashoggi was dead. "It's very sad."

Trump, who spoke to reporters prior to departing for a campaign rally in Montana, added that the United States will be making "a very strong statement" after investigations are complete. "It will have to be very severe."

Earlier Thursday, US Treasury Secretary Steven Mnuchin said he will not attend the Future Investment Initiative summit in Saudi Arabia. Mnuchin said on Twitter he made the decision after meeting with Trump and Secretary of State Mike Pompeo.

Mnuchin joins top US executives, including JP Morgan chief executive Jamie Dimon and Ford chairman Bill Ford, who have decided not to attend the conference in the wake of Khashoggi's disappearance, according to US news reports.

The heads of other multinational companies, the World Bank and the International Monetary Fund also have pulled out, and several US media firms, including CNN, CNBC, the New York Times, the Economist and Financial Times, have pulled their sponsorship.

Fox Business News announced Thursday it has withdrawn as a sponsor of the conference "amid growing concerns about the kingdom’s involvement in the death of Washington Post columnist Jamal Khashoggi."

The conference, which is scheduled to take place in Riyadh later this month, is a showcase event for the government. Global corporations had planned to send executives to the conference in search of investment opportunities in Saudi Arabia, where the leadership has been pursuing a strategy of diversifying its oil-based economy.

Mnuchin's decision came shortly after Pompeo said the US would wait for Saudi Arabia and Turkey to complete their investigations into Khashoggi's disappearance.

The US believes that "a complete picture will emerge" after the investigations are finished, Pompeo said after briefing Trump about his trip this week to Saudi Arabia and Turkey to discuss the Khashoggi case.

Investigators should be granted "a few more days" to complete their work, he said, stressing Saudi Arabia's role as "an important counterterrorism partner."

The Turkish government expects to see the results of its investigation soon, Justice Minister Abdulhamit Gul said earlier on Thursday.

"We all expect the probe to be concluded as soon as possible," Gul told state news agency Anadolu, characterizing the investigation as "very careful and successful." A team concluded its search of the Saudi consulate and the consul's residence early Thursday.

Khashoggi, a vocal critic of Saudi Arabia's powerful Crown Prince Mohammed bin Salman, was last seen entering the Saudi consulate in Istanbul on October 2, where he had gone to pick up papers so he could marry his Turkish fiancee.

Turkish officials have told the media that Khashoggi, a columnist for the Washington Post, was murdered inside the consulate. Saudi Arabia has denied the allegations.

Gul urged people to ignore leaks regarding the Khashoggi case, including images and the names of alleged hitmen in pro-government media outlets, as well as apparent audio recordings.

Anadolu on Thursday published an article accusing the Saudi leadership of failing to cooperate with Ankara on the probe and raised questions on the lack of surveillance video recordings. It also speculated that the Saudis are preparing to "confess" to the alleged assassination of Khashoggi.

Turkish officials earlier confirmed that 15 Saudi citizens entered the consulate building minutes after Khashoggi. It remains unclear why the 15 people, some of them identified by Anadolu as senior Saudi soldiers and forensic experts, were there.