A diplomatic vehicle belonging to the Saudi consulate has been discovered abandoned on the outskirts of Istanbul, days after the killing of journalist Jamal Khashoggi.

Security sources told Turkey's state TV the vehicle was found in the Sultangazi district, some way outside the city centre.

Turkish crime scene investigators have arrived at the underground car park in which the vehicle was reportedly dumped days after Mr Khashoggi's murder at the hands of a 15-man Saudi squad of intelligence and security officials, according to local media. Officials also released to state television a photo of an unidentified man entering and leaving the vehicle, a black 2011 E-Series Mercedes-Benz sedan, "days" after the killing, state TV reported.

Still from Turkey's state-owned TRT shows mysterious man parking and leaving a Saudi consular vehicle in underground garage park on Istanbul's outskirts. (TRT)

Saudi officials have insisted the killing was the result of a botched attempt to convince Mr Khashoggi to return to Saudi that resulted in a panicked attempt to cover up the slaying from both Turkish authorities and Saudi leaders. But the vehicle hints at a far wider and complex coverup scheme encompassing a larger swath of Istanbul's geography, a longer time frame that stretched well past Mr Khashoggi's 2 October death, and more personnel than the 15-man Saudi team that has been exposed by Turkish media.

"Turkish officials are 100 per cent sure that this wasn’t a botched operation or rogue operation," Ragip Soylu, Washington correspondent for the pro-government Daily Sabah newspaper, told The Independent. "The fact that this team arrived in a sophisticated way on the day of murder tells us that it was premeditated. Obviously Saudis were tying to cover their tracks by using many cars. Even on the day of arrival to consulate, they used seven different cars. At an operational level, they were trying to do job by the book, but botched the details."

Turkey has accelerated leaks from the investigation into Khashoggi's killing ahead of much-anticipated speech tomorrow during which President Recep Tayyip Erdogan has vowed to disclose fresh details. Police reportedly requested permission to search the car from the chief public prosecutor's office and the consulate general of Saudi Arabia. It is not clear if their request has been granted.

Investigators looking into the disappearance of Khashoggi last week searched other consulate vehicles, along with the consulate building and the consul general's residence.

Saudi Arabia said on Saturday Khashoggi was killed in a "fistfight" inside the consulate. Turkish media and officials say the 59-year-old Washington Post columnist was attacked by a 15-man Saudi team that cut off his fingers and decapitated him.

Car with diplomatic plates allegedly belonging to Saudi Consulate seen in an Istanbul car park (REUTERS)

His remains have yet to be found.

The disclosure of the abandoned car comes on the same day as reports of a man appearing to wear Khashoggi's clothes can be seen on surveillance video leaving the Saudi consulate after the journalist's death.

CNN aired surveillance footage showing a man in Mr Khashoggi's dress shirt, suit jacket and trousers.

At 57 years old, the alleged decoy, Mustafa Muhammed al-Madany, was the oldest member by a dozen years of the team apparently dispatched to Turkey from Riyadh to confront the 59-year-old journalist.

Trump says he is not satisfied with Saudi account of journalist Jamal Khasoggi's death

Mr al-Madany is seen in the footage walking out of the consulate via its back exit with an accomplice, then taking a taxi to Istanbul's famed Sultan Ahmed Mosque, where he went into a public toilet, changed back out of the clothes and left.

The state-run broadcaster TRT also reported that a man who entered the consulate building was seen leaving the building in Mr Khashoggi's clothes.

In the days after Khashoggi vanished, Saudi officials initially said that he had left the consulate.

Citing unnamed government sources, the newspaper Yeni Safak reported on Monday that the Saudi crown prince Mohammed bin Salman had got on the phone with Mr Khashoggi during a consular visit to obtain personal papers and personally attempted to convince him to return to the kingdom.

The claim could not be verified but other sources have told The Independent that at least some parts of Mr Khashoggi’s encounter in the consulate may have been live streamed to Riyadh.

Khashoggi disappearance: Forensic police investigate Saudi consul Show all 12 1 /12 Khashoggi disappearance: Forensic police investigate Saudi consul Khashoggi disappearance: Forensic police investigate Saudi consul According to local media reports, Saudi consul Mohammad al-Otaibi left Turkey on 16 October. A Turkish prosecutor on 15 October has entered the Saudi consulate in Istanbul to investigate the disappearance of dissident Saudi journalist Jamal Khashoggi, an inspection that was being carried out jointly with a Saudi team AFP/Getty Images Khashoggi disappearance: Forensic police investigate Saudi consul Turkish forensic police officers work on the roof of the residence of the Saudi consul in Istanbul EPA Khashoggi disappearance: Forensic police investigate Saudi consul Khashoggi went missing on 2 October when he entered the Saudi consulate to pick up paperwork AP Khashoggi disappearance: Forensic police investigate Saudi consul ISTANBUL, TURKEY - OCTOBER 17: Turkish police arrive to investigate the Saudi Arabian consulate general residence as investigations continue into the disappearance of journalist Jamal Khashoggi on October 17, 2018 in Istanbul, Turkey. Turkish police first entered and searched the Saudi Arabian consulate on October 15 amid a growing international backlash about the disappearance. Khashoggi, a U.S. resident and critic of the Saudi regime, has been missing since visiting the Saudi Arabian consulate on October 2. Turkish officials have said they believe he was killed inside. (Photo by Chris McGrath/Getty Images) ***BESTPIX*** Chris McGrath Khashoggi disappearance: Forensic police investigate Saudi consul Turkish forensic and investigation officers arrive at Saudi Consul's residence on October 17, 2018 in Istanbul. - Saudi Arabia's consul to Istanbul Mohammed al-Otaibion on October 16, 2018 left the Turkish city bound for Riyadh on a scheduled flight, reports said, as Turkey prepared to search his residence in the probe into the disappearance of journalist Jamal Khashoggi. (Photo by OZAN KOSE / AFP)OZAN KOSE/AFP/Getty Images OZAN KOSE AFP/Getty Images Khashoggi disappearance: Forensic police investigate Saudi consul Turkish police arrive to investigate the Saudi Arabian consulate general residence Getty Images Khashoggi disappearance: Forensic police investigate Saudi consul Turkish forensic police search for evidence at the garden of the Saudi Arabia's Consul General Mohammad al-Otaibi AFP/Getty Images Khashoggi disappearance: Forensic police investigate Saudi consul Turkish police search the rooftop of the Saudi Arabian consulate general residence Getty Images Khashoggi disappearance: Forensic police investigate Saudi consul Turkish police arrive at the residence of the Saudi consul General Mohammed al-Otaibi to conduct a search AP Khashoggi disappearance: Forensic police investigate Saudi consul Turkish police officers gather as they prepare to enter Saudi Arabia consul's residence, in Istanbul, Wednesday, Oct. 17, 2018. America's top diplomat is in Turkey, where a strongly pro-government newspaper has published a gruesome recounting of the alleged slaying of Saudi writer Jamal Khashoggi at the Saudi Consulate in Istanbul. (AP Photo/Petros Giannakouris) Petros Giannakouris AP Khashoggi disappearance: Forensic police investigate Saudi consul Turkish forensic police search for evidence at the garden of the Saudi Arabia's Consul General Mohammad al-Otaibi AFP/Getty Images Khashoggi disappearance: Forensic police investigate Saudi consul ISTANBUL, TURKEY - OCTOBER 17: Turkish police search the rooftop of the Saudi Arabian consulate general residence as investigations continue into the disappearance of journalist Jamal Khashoggi on October 17, 2018 in Istanbul, Turkey. Turkish police first entered and searched the Saudi Arabian consulate on October 15 amid a growing international backlash about the disappearance. Khashoggi, a U.S. resident and critic of the Saudi regime, has been missing since visiting the Saudi Arabian consulate on October 2. Turkish officials have said they believe he was killed inside. (Photo by Chris McGrath/Getty Images) Chris McGrath Getty Images

White House adviser Jared Kushner said on Monday he had urged the crown prince to be transparent about the killing of Jamal Khashoggi, and told him “the world is watching” Riyadh's account of the journalist's disappearance.

At times, President Donald Trump appeared at times to play down Riyadh's role in the incident, but also warned of potential economic sanctions. He has repeatedly highlighted the kingdom's importance as an ally.

Mr Kushner, Trump's son-in-law and senior adviser, has cultivated a personal relationship with Prince Mohammed and urged Trump to act with caution to avoid upsetting a critical strategic and economic relationship, a senior administration official said.

“Just to be transparent, to be fully transparent. The world is watching. This is a very, very serious accusation and a very serious situation,” Mr Kusher said he had told the crown prince.

Asked how the prince responded, Mr Kushner, speaking on CNN, said: “We'll see.”

Mr Kushner said the United States was in a “fact-finding phase” on the case and had its “eyes wide open”. He did not say when or by what means he had communicated with Crown Prince Mohammed.

Turkish president Recep Tayyip Erdogan has promised to detail Khashoggi's killing, raising international pressure on Saudi Arabia.

Pro-government newspapers have been drip-feeding information about the killing, apparently with the help of Turkish security forces.

"We seek justice and this will be revealed in all its naked truth, not through some ordinary steps but in all its naked truth,” Mr Erdogan said at the opening of an Istanbul mass transit line expansion on Sunday. “This is not an ordinary case. The incident will be revealed entirely.”

Saudi Arabia has sought to depict the killing of Khashoggi as an unintended death that took place during an attempt to convince him to come home as part of an authorised program to draw dissidents back to the kingdom.