Saudi special forces officers, intelligence officials, national guards and a forensics expert were allegedly among a 15-person team tied to the disappearance in Istanbul of the high-profile dissident Jamal Khashoggi, it has been reported by Turkish pro-government newspapers.

The details of the alleged hit squad were listed on flight manifests leaked to Turkish media. Social media profiles of some of the alleged suspects link them to elite sections of the Saudi security apparatus.

Meanwhile, investigators are turning their focus towards the underground garage of the Saudi consul general’s home, where the cars thought to have carried Khashoggi are believed to have to have been driven immediately after they left the nearby consulate.

Profile Who was Jamal Khashoggi? Show Hide Jamal Khashoggi was one of the Arab world’s most prominent journalists and commentators. He was an outspoken critic of Saudi Arabia who dared to defy Crown Prince Mohammed bin Salman. While living in Saudi Arabia, Khashoggi was told to stop writing or posting on Twitter, where he had more than 1.6 million followers. He moved to the US in June 2017, where he continued to comment on his country both in print and on television. He wrote columns for the Washington Post and the Guardian.

His message struck a nuanced tone in the US, where he tried to acknowledge the reforms undertaken by Bin Salman while also highlighting the flaws. Khashoggi previously had close links with the Saudi royal family, including having served as a media aide to Prince Turki al-Faisal, when the latter was director general of the Saudi intelligence agency. He was also a former editor of the Saudi newspaper al-Watan and had worked with Prince Alwaleed bin Talal, a grandson of the first Saudi king. Khashoggi was murdered in the Saudi Arabian consulate in Istanbul in October 2018. Photograph: Virginia Mayo/AP

Investigators also disclosed on Wednesday that they were focusing on an Apple watch that Khashoggi was wearing that was connected to an iPhone he had left with his fiancee outside the consulate. “We have determined that it was on him when he walked into the consulate,” a security official told Reuters. Investigators are seeking to determine what information the watch had transmitted.

Donald Trump said that the US was “demanding” answers from the Saudi government and working closely with Turkey to find out what happened to the missing dissident.

“It’s a very serious situation for us and for this White House,” he told reporters on Wednesday. “I want to see what happens and we’re working very closely with Turkey and I think we’ll get to the bottom of it.”

The US president also said that he had invited Khashoggi’s fiancee, Hatice Cengiz, to the White House.

Mike Pompeo, the US secretary of state, John Bolton, the national security adviser, and Trump’s son-in-law, Jared Kushner, all spoke to the Saudi Arabian crown prince, Mohammed Bin Salman, to request further information about the missing journalist, according to the White House spokeswoman Sarah Sanders.

Twenty-two US senators signed a letter to Trump on Wednesday triggering an investigation and determination of whether human rights sanctions should be imposed over Khashoggi’s disappearance.

In the letter, the senators said they had triggered a provision of the Global Magnitsky Human Rights Accountability Act requiring the president to determine whether a foreign person is responsible for a gross human rights violation.

Turkish officials remain convinced that Khashoggi was killed by the alleged hit squad inside the consulate building – a view partly formed by security footage, much of which has not been released. But, unlike the roads outside the diplomatic mission, they have no camera coverage of the consul general’s residence or the garage beneath it, and say the cars and their occupants remained out of sight for several hours before continuing to Atatürk airport.

Details of the Saudi citizens who travelled to Istanbul were released amid a claim that they had brought with them a bone saw to dismember Khashoggi. “It was like Pulp Fiction,” a Turkish official told the New York Times. Suggestions that Khashoggi was killed and his body then mutilated have gained wide circulation in the week since he vanished, and Turkish officials continue to insist he met a brutal fate when he stepped through the doors of the diplomatic mission.

The alleged involvement of a forensics expert adds weight to the suspicions. The passenger manifest, obtained by the pro-government Daily Sabah newspaper, also lists a senior intelligence officer and two Saudi air force officers.

The Saudi team is said to have arrived at Atatürk airport on Tuesday last week on two planes, one of which landed in the pre-dawn hours and the second in the early afternoon. Airport security officials now say they checked all bags that the Saudi teams took with them to the airport and say there were nothing suspicious in any of the items loaded on to the jets for their return journeys to Riyadh.

Officials also said they had become aware that Khashoggi may have been kidnapped before the second plane had departed, and monitored seven Saudis in a waiting room as they checked their luggage for a second time. When nothing unusual was discovered, the plane was allowed to leave.

Turkish media have broadcast CCTV footage that shows the alleged Saudi team arriving and leaving Istanbul airport, as well as vehicles approaching and leaving the consulate.

On Wednesday evening, the Washington Post cited US intelligence intercepts to report that Saudi Arabia’s crown prince had ordered an operation targeting Khashoggi. The paper reported unnamed US officials saying Saudis had been heard discussing a plan to lure the journalist from Virginia and detain him.

A state department spokesman earlier insisted the US had no forewarning on any threat.

The Turkish president, Recep Tayyip Erdoğan, has promised a transparent investigation into Khashoggi’s fate. However, many officials who provided information earlier in the inquiry are now refusing to speak, citing political sensitivities.

Turkey had in recent days attempted to offer Riyadh a way to de-escalate a crisis that continues to gather momentum outside the region by suggesting that a “deep state” and not senior Saudi officials were responsible for Khashoggi’s disappearance. However, there has been little interest from the kingdom, leading some senior Turkish officials to conclude that Riyadh does not fear the consequences.

Facebook Twitter Pinterest Protesters in Istanbul hold pictures of missing journalist Jamal Khashoggi on Monday. Photograph: Ozan Köse/AFP/Getty Images

“If it’s confirmed Riyadh is responsible for Khashoggi’s death, this could be their Crimea moment,” said HA Hellyer, senior nonresident fellow at the Atlantic Council and the Royal United Services Institute in London. “Russia annexing Crimea caused justifiable huge uproar internationally, but in the end not very much happened to Putin or Russia.”

Khashoggi was last seen a week ago entering the consulate in Istanbul to get documents related to his forthcoming marriage.

Khashoggi case is test for UK-Saudi relationship | Patrick Wintour Read more

The disappearance of the acclaimed columnist and senior adviser to previous Saudi regimes has rocked Washington, where he had been based for the past year as a columnist for the Washington Post, and struck fear through establishment circles in Riyadh, where the 59-year-old had been a popular figure.

He was one of the few public intellectuals to openly critique the new administration of Prince Mohammed. The Saudi government has denied any involvement in Khashoggi’s disappearance and said he left the consulate via a back entrance. Last week Prince Mohammed told Bloomberg that his government was “very keen to know what happened to him”.

On Tuesday Cengiz used an opinion piece for the Washington Post to appeal to Trump for help to “shed light” on the disappearance. “I also urge Saudi Arabia, especially King Salman and Crown Prince Mohammed bin Salman, to show the same level of sensitivity and release CCTV footage from the consulate,” she wrote.