Turkey's investigation into the disappearance of prominent Saudi journalist Jamal Khashoggi has revealed recordings made on his Apple Watch purportedly indicate he was tortured and killed, a Turkish newspaper reported on Saturday.

A Turkish newspaper says it has recordings which prove a Saudi journalist was tortured and killed.

The country is investigating the disappearance of Jamal Khashoggi.

The pro-government paper, Sabah daily, says the footage is from the dissident's Apple Watch.

And that the watch synched with the journalist's iphone, which his fiancee was carrying outside Istanbul's Saudi consulate as she waited for him to emerge.

Reuters has been unable to verify the report.

Khashoggi, an outspoken critic of the Saudi government, has not been seen since October 2nd.

He entered the country's consulate in Istanbul to get documents for his impending marriage.

Saudi officials say he left shortly afterwards.

But Turkish officials and his fiancee, who was waiting outside, say he never came out.

Both countries have agreed to carry out a joint investigation into his disappearance.

Turkish sources have told Reuters the police believe Khashoggi was deliberately murdered inside the consulate.

Riyadh has dismissed the claims as "lies and baseless allegations".

Technology experts say it is highly unlikely the Apple watch could have recorded actions inside the embassy and then uploaded them to an iCloud account.

Most models of the gadget need to be within 9-15 metres of the iPhone it's paired with for this to work.

Even newer models that can communicate with the cloud directly via wireless need connections that aren't available in Turkey.

Turkey's Sabah newpaper believes Khashoggi turned on the recording feature on the watch before entering the consulate.

It cites "reliable sources in a special intelligence department" and alleges Saudi agents used his fingerprint to unlock the phone after he died and deleted some files, but not all of them.