Two senior Turkish officials have revealed the existence of an object that may provide important clues to Jamal Khashoggi's fate: the black Apple Watch he was wearing when he entered the Saudi Arabian consulate in Istanbul.

Key points: Mr Khashoggi may have recorded goings-on in the Saudi consulate on his watch

Mr Khashoggi may have recorded goings-on in the Saudi consulate on his watch Audio exists of Mr Khashoggi being interrogated, tortured and murdered, according to the Washington Post

Audio exists of Mr Khashoggi being interrogated, tortured and murdered, according to the Washington Post US officials say they are seeking answers from the Saudi Government

The missing journalist's watch was connected to a mobile phone he left outside when he entered the building on October 2, they said.

Mr Khashoggi, a forceful critic of the Saudi government, went missing after he entered the consulate, and Turkish officials have said they believe he was murdered there.

A senior Turkish government official and a senior security official said the two interconnected devices are at the heart of the investigation into Mr Khashoggi's disappearance.

"We have determined that it was on him when he walked into the consulate," the security official said.

Turkish officials say they believe Jamal Khashoggi was killed inside the Saudi consulate in Istanbul. ( AP: Hasan Jamali, file )

Investigators are trying to determine what information the watch transmitted.

"Intelligence services, the prosecutor's office and a technology team are working on this. Turkey does not have the watch so we are trying to do it through connected devices," he said.

Tech experts say an Apple Watch can provide data such as location and heart rate.

But what investigators can find out depends on the model of watch, whether it was connected to the internet, and whether it is near enough an iPhone to synchronise.

US officials say they are seeking answers from the Saudi Government and are not yet accepting the Turkish Government's conclusions.

Meanwhile, the Washington Post reported that the Turkish Government has told US officials it has audio and video recordings that prove the journalist was killed inside the embassy.

"The voice recording from inside the embassy lays out what happened to Jamal after he entered," one person with knowledge of the recording said, speaking on the condition of anonymity, the Washington Post reported.

Questions remain over what happened to Mr Khashoggi inside the Saudi consulate. ( AP: Lefteris Pitarakis )

"You can hear his voice and the voices of men speaking Arabic," the person said.

"You can hear how he was interrogated, tortured and then murdered."

A second person briefed on the recording said men could be heard beating Mr Khashoggi, according to the Post.

Fifteen Saudi men at centre of investigation

Sorry, this video has expired Investigators could still find clues at the consulate, says FBI veteran Martin Reardon

Two Turkish security sources said security camera recordings showed Mr Khashoggi had not left the consulate by either of its two exits.

They said that 15 Saudi men had entered the building at around the time Mr Khashoggi went in, having flown into Istanbul earlier in the day, most of them on a private aircraft from Riyadh and some on commercial flights.

The men left after "some time" in two cars and returned to the airport, the sources said.

They said a third vehicle left at the same time but turned in the opposite direction. Investigators are trying to trace its route by analysing surveillance cameras.

The Istanbul consulate referred questions about the 15 men and the vehicles to Saudi authorities, who did not respond to a request for comment.

"It is a very mysterious situation. Diplomats that came in private jets, stay in Turkey for a few hours, and leave. It is also very easy for them to pass through security due to their diplomatic immunity," one of the security sources said.

ABC/wires