Turkey's Foreign Ministry says authorities will search Saudi Arabia's consulate in Istanbul in connection with the disappearance of Saudi journalist Jamal Khashoggi.
A ministry statement said Saudi Arabia indicated it was open to cooperation, but there were no details about when the search would take place.
Turkey said the investigation is being conducted "in an intense manner."
Turkish police are looking into two private aircraft that landed at the Istanbul airport a week ago that were believed to be carrying 15 Saudis of interest in the case, along with the possibility that Khashoggi might have been kidnapped and taken aboard one of the planes.
The Turkish daily newspaper Sabah reported that both planes returned to Riyadh, with one stopping first in Dubai and the other in Egypt. The planes belonged to a Saudi company with links to the government.
The newspaper said Turkish employees at the consulate were "hastily" told to take a holiday on the day that Khashoggi was there.
Khashoggi has not been seen since entering the consulate last week. Turkish officials have said he was murdered there, while Saudi Arabia says he safely left the building and have called the allegations that he was killed "baseless."
But the the Saudis have offered no evidence to show he left the building, nor have Turkish officials offered proof that he was killed.
U.S. President Donald Trump told reporters at the White House he plans to talk to the Saudis about the case, but had no information about Khashoggi's fate.
Turkish President Recep Tayyip Erdogan said Saudi officials need to prove that Khashoggi left the building after arriving last Tuesday to get a document for his upcoming marriage. His Turkish fiancee, Hatice Cengiz, who waited for him outside the consulate, said he never came out of the building.
"We have to get an outcome from this investigation as soon as possible. The consulate officials cannot save themselves by simply saying 'he has left,'" Erdogan said Monday on a visit to Budapest.
Saudi Crown Prince Mohammed bin Salman said last week Riyadh was "ready to welcome the Turkish government to go and search our premises," because it had "nothing to hide" about the missing journalist.
Khashoggi, who had been critical of the Salman government, has been living for a year in self-imposed exile in the United States after a Riyadh crackdown on dissent in the kingdom.
Protesters have gathered outside the Saudi consulate demanding to know what had happened to Khashoggi. Banners read, "We will not leave without Jamal Khashoggi."
U.S. Secretary of State Mike Pompeo called on Saudi Arabia to support a thorough, transparent investigation.
"We have seen conflicting reports on the safety and whereabouts of prominent Saudi journalist and Washington Post contributor Jamal Khashoggi," Pompeo said in a statement late Monday. "State Department senior officials have spoken with the Kingdom of Saudi Arabia through diplomatic channels about this matter."
His comments came hours after U.S. President Donald Trump expressed concern about the situation.
"Right now, nobody knows anything about it.I do not like it," Trump told reporters at the White House.
U.S. Republican Senator Lindsey Graham said he and other lawmakers "agree if there was any truth to the allegations of wrongdoing by the Saudi government, it would be devastating to the U.S.-Saudi relationship and there will be a heavy price to be paid - economically and otherwise."
A Turkish official told the Reuters news agency "the initial assessment of the Turkish police is that Mr. Khashoggi has been killed at the consulate of Saudi Arabia in Istanbul. We believe that the murder was premeditated and the body was subsequently moved out of the consulate."