The United States warned Friday of a "wide range" of responses should it determine that Saudi Arabia is behind the disappearance and apparent death of journalist Jamal Khashoggi, as Turkey widened its investigation into the scandal.
President Donald Trump said that the United States, which is Saudi Arabia's biggest backer, could impose sanctions over the feared murder of Khashoggi.
His top diplomat Mike Pompeo told Voice of America Radio: "We'll certainly consider a wide range of potential responses."
The Trump administration has been notably slow to criticize Saudi Arabia, despite mounting evidence that Khashoggi, a critic of the Islamic petro-state's powerful crown prince, vanished after entering the Saudi consulate in Istanbul.
The Khashoggi case has presented Trump with one of the most acute foreign policy crises of his nearly two-year-old presidency.
"I will very much listen to what Congress has to say," Trump said in Arizona, adding that it was too early to draw conclusions.
"Could be," he said of possible sanctions. "We are going to find out who knew what -- and when."
Trump on Thursday said for the first time that Khashoggi, who wrote for The Washington Post, was probably dead and warned of a "severe" response.
Pompeo said that during a trip he made this week to meet Saudi leaders in Riyadh, "I made very clear to them that the United States takes this matter very seriously, that we don't approve of extrajudicial killings."
- Forest search -
Turkish authorities widened their probe, searching a forest in the city and interviewing the consulate's staff.
Pro-government Turkish media have repeatedly claimed that Khashoggi was tortured and decapitated by a Saudi hit squad inside the diplomatic mission, although Turkey has yet to divulge details about the investigation.
But the controversy has already put the kingdom -- for decades a key Western ally and bulwark against Iran in the Middle East -- under unprecedented pressure amid reports it is scrambling to provide an explanation to take the heat off its rulers.
It is also a major crisis for Crown Prince Mohammed bin Salman, a Trump administration favorite who has portrayed himself as a modernizing Arab reformer, but whose image and even position at home could now be gravely undermined.
Close ally the United Arab Emirates warned the controversy should not be exploited to "destabilize" Saudi Arabia.
- Turkish employees testifying -
Fifteen staff, all Turkish nationals, testified at the chief prosecutor's office, state-run news agency Anadolu said. It has been reported that Turkish employees were given the day off on October 2, the day Khashoggi disappeared.
Among those giving statements inside Istanbul's main courthouse were the consulate driver, technicians, accountants and receptionists.
Istanbul's Belgrad forest became a target of the investigation after police focused on the vehicles that had left the consulate on the day Khashoggi disappeared, NTV television reported. At least one vehicle is suspected to have gone to the forest.
The forest, a vast area sufficiently remote for even locals to regularly get lost there, is some nine miles (15 kilometers) from the consulate.
Investigators already conducted two searches of the consulate and a nine-hour search of the consul's residence this week.
Pro-government daily Sabah published new CCTV images of some of the Saudi team arriving in Istanbul and reported that two of the men landed in the city on October 1.
Previously, local media said the 15 men arrived in Turkey on October 2 on two private planes.
Foreign Minister Mevlut Cavusoglu did not reveal probe details but promised to share information in due course "in a transparent manner."
"It is out of the question for us to share this or that information with any country," he said.
- 'No tape given' -
The key potential piece of evidence in the investigation is an alleged audio tape whose existence has been reported by pro-government media. They say it proves Khashoggi was tortured and then killed.
ABC News quoted an unnamed Turkish official as saying Pompeo heard the audio tape and was shown a transcript of the recording during his visit to Ankara.
But Pompeo said he had neither "seen" nor "heard" a tape and had not read a transcript while in Ankara, where he met with President Recep Tayyip Erdogan and Cavusoglu.
Cavusoglu also denied the claims and said it was "out of the question for Turkey to give any kind of audio tape to Pompeo or any other US official."
Trump weighed in on the matter, tweeting the report was "FAKE NEWS!" and Pompeo "was never given or shown a Transcript or Video of the Saudi Consulate event."
- US gives Saudi more time -
The New York Times reported that Saudi leaders could blame General Ahmed al-Assiri, a top intelligence official close to the crown prince.
Previously, US media said the Saudis were preparing a report that Khashoggi's death resulted from a botched interrogation.
As Washington seeks to avoid a long-term rupture with its ally Riyadh, Pompeo told Trump the Saudis should be given "a few more days to complete" an official probe.
The furor has also blown a huge hole in next week's Future Investment Initiative conference in Riyadh.
It was meant to showcase Prince Mohammed's plans for reform but has now been hit by a stream of big name cancellations, including US Treasury Secretary Steven Mnuchin.