Saudi Arabia's Foreign Minister Adel al-Jubeir said Sunday the kingdom did not know where the body of slain journalist Jamal Khashoggi was, despite admitting to the killing and calling it a “tremendous mistake.”

Speaking in an interview on Fox News, Jubeir said the Saudi leadership initially believed Khashoggi had left its consulate in Istanbul, where he was last seen on October 2.

But following “reports we were getting from Turkey,” Saudi authorities began an investigation, which discovered he was killed in the diplomatic mission.

“We don't know, in terms of details, how. We don't know where the body is,” Jubeir said, adding that the Saudi public prosecutor had put out orders to detain 18 individuals, “the first step in a long journey.”

He termed the killing a “tremendous mistake” but one which the US-Saudi relationship would eventually overcome.

“The individuals who did this did this outside the scope of their authority. There obviously was a tremendous mistake made, and what compounded the mistake was the attempt to try to cover up,” Jubeir told Fox News.

“That is unacceptable in any government. These things unfortunately happen. We want to make sure that those who are responsible are punished and we want to make sure we have procedures in place to prevent it from happening again. “

Turkey to reveal details of probe

In a sign of growing pressure on Saudi Arabia, Turkey said it will announce details of its investigation into the killing of journalist Jamal Khashoggi on Tuesday and US congressional leaders said the Gulf kingdom in particular its crown prince should face severe consequences for the death of the writer in the Saudi consulate in Istanbul.

The announcement on Sunday by Turkish President Recep Tayyip Erdogan that he will “go into detail” about the Khashoggi case in a speech in parliament heightened hopes for some clarity in a case that has been shrouded in mystery, conflicting accounts and shocking allegations.

Erdogan spoke after Saudi Arabia, in a statement early Saturday, finally acknowledged that 59-year-old Khashoggi had died in the consulate, though its explanation that he was killed involuntarily in a “fistfight” was met with international skepticism and allegations of a cover-up designed to absolve Prince Mohammed of direct responsibility.

Saudi Arabia said 18 Saudis were arrested and that several top intelligence officials were fired.

Pro-government media in Turkey have reported a different narrative, saying a Saudi hit squad of 15 people traveled to Turkey to kill the columnist for The Washington Post before leaving the country hours later in private jets.

“Why did these 15 people come here? Why were 18 people arrested? All of this needs to be explained in all its details,” Erdogan said.

Meanwhile, Istanbul's chief prosecutor summoned 28 more staff members of the Saudi consulate, including Turkish citizens and foreign nationals, to give testimony on Monday, Turkish state broadcaster TRT reported.

Prosecutors have previously questioned consulate staff; some Turkish employees reportedly said they were instructed not to go to work around the time that Khashoggi disappeared.

Also, on Sunday, images that were obtained by TRT World, a Turkish news channel that broadcasts in English, showed Khashoggi as he arrived at a police barrier before entering the consulate on October 2. The images, taken from security camera video, show the writer being searched before continuing toward the building.