Turkey on Friday widened the investigation into the disappearance of journalist Jamal Khashoggi after his visit to the Saudi consulate, searching a forest in the city.

Ankara also denied giving any audio recording to US officials from the investigation about Khashoggi, a former royal insider who moved to the United States after becoming a critic of the current House of Saud leadership.

US President Donald Trump acknowledged that Khashoggi was likely dead even as his fate remained unclear 17 days after he vanished.

Pro-government Turkish media have provided a steady stream of claims that Khashoggi was tortured and decapitated by a Saudi hit squad inside the consulate, 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 favourite of the Trump administration who has portrayed himself as a modernising Arab reformer, but whose image and even position at home could now be gravely undermined.

Forest search

Istanbul's Belgrade forest became a target of the investigation after police focused on the vehicles which had left the consulate on the day Khashoggi disappeared, NTV channel reported. At least one vehicle is suspected to have gone to the forest.

The forest, a vast area and sufficiently remote for even locals to regularly get lost there, is nearly 15 kilometres (over nine miles) away from the Saudi consulate.

Investigators already conducted two searches of the consulate and a nine-hour search of the consul's residence this week. The Saudi consul, Mohammed al-Otaibi, abruptly left Istanbul for Riyadh on Tuesday.

Pro-government daily Sabah on Friday 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 the day that Khashoggi went missing via two private planes, which then returned to Riyadh via Egypt and Dubai.

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 during a visit to Albania's capital, Tirana.

'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 on Thursday quoted an unnamed Turkish official saying US Secretary of State Mike 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 during the visit to Ankara where he held talks with President Recep Tayyip Erdogan and Cavusoglu.

Read: ‘This has not been business as usual in my country’: excerpts from Saudi journalist Khashoggi’s writings

Cavusoglu on Friday 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”.

Earlier Trump said he now believed Khashoggi was dead and warned of “very severe” consequences should Saudi Arabia be proven responsible.

“It certainly looks that way to me. It's very sad,” Trump said when asked if he believed that Khashoggi is no longer alive.

'Prevent whitewash'

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 Saudis were preparing a report that Khashoggi's death resulted from a botched interrogation, in a bid to limit the global backlash against Riyadh and damage to the crown prince.

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.

But four prominent human rights and press freedom groups urged Turkey to demand a United Nations investigation to prevent a “whitewash” of the alleged crime.

The furore 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.