The White House said Wednesday that top Trump administration officials have spoken to Saudi Crown Prince Mohammed bin Salman about the mysterious disappearance of Saudi journalist Jamal Khashoggi, whom Turkish officials say they believe was murdered last week inside Riyadh's consulate in Istanbul.
SEE ALSO: UN Demands Probe Into 'Shocking' Disappearance of Saudi Journalist
National security adviser John Bolton and senior adviser Jared Kushner, President Donald Trump's son-in-law, talked with Salman on Tuesday, while Secretary of State Mike Pompeo had a follow-up call with the Saudi leader to reiterate the U.S. demand for information about the case, the White House said.
'In both calls they asked for more details and for the Saudi government to be transparent in the investigation process,' the White House said.
FILE - An official leaves the Saudi Arabia consulate in Istanbul, Oct. 7, 2018.
Spokeswoman Sarah Sanders said the U.S. is continuing to monitor the unfolding investigation in Istanbul, but offered no information about what the crown prince told the U.S. officials regarding Khashoggi's disappearance.
Trump told reporters he had talked with officials in Saudi Arabia 'at the highest level' about Khashoggi's disappearance, but offered no indication on his whereabouts.
'It's a very sad situation, this is a bad situation,' Trump said. 'It's a terrible thing.'
'Nobody knows what happened,' Trump said, adding, 'We want to get to the bottom of it. We cannot let this happen, to reporters, to anyone.'
Trump declined to say whom he talked with in the Saudi government. He said his aides have been in contact with Khashoggi's fiancee, Hatice Cengiz, and hope to set up a meeting with her at the White House.
Turkish officials say they believe Khashoggi, a critic of Salman who has been living in self-imposed exile in the U.S., either was murdered October 2 inside the consulate when he went there to pick up documents to allow him to marry Cengiz, a Turkish national, or was spirited away to Riyadh.
A demonstrator dressed as Saudi Arabian Crown Prince Mohammed bin Salman, center, with blood on his hands protests with others outside the Saudi Embassy in Washington, Oct. 10, 2018.
Saudi Arabia has called the allegation 'baseless,' but has offered no proof that Khashoggi left the consulate alive, nor has Turkey produced evidence that he was killed inside the diplomatic outpost.
Vice President Mike Pence, asked if Washington might dispatch FBI technicians if Saudi Arabia requested it, said, 'I think the United States of America stands ready to assist in any way.'
Pence did not indicate that either Turkey, which has launched an intensive investigation into Khashoggi's disappearance, or Saudi Arabia has sought U.S. assistance.
He told conservative talk show host Hugh Hewitt that Khashoggi's disappearance is 'a great concern for the United States of America. The suggestion that this journalist, Mr. Khashoggi, was you know, was murdered should be deeply troubling to everyone that cares as a free and open press around the world. ... The free world deserves answers. Violence against journalists should be condemned, but at this point, we don't know what happened.'
A key U.S. lawmaker, Senator Tim Kaine of Virginia, told VOA the unfolding drama could significantly affect U.S. relations with Saudi Arabia, long an American ally in the Middle East.
'If it turns out that suspicions of Saudi involvement in the murder of this journalist are true,' Kaine said, 'it could be a real sea-change in the relationship between the U.S. and Saudi Arabia that could affect many things, including U.S. support for what Saudi Arabia is doing in Yemen. So I think we have to get to the bottom of it.'
Turkey has focused much of its investigation on 15 Saudi nationals who arrived in Istanbul on two flights the same day as Khashoggi was at the consulate.
FILE _ This image taken from CCTV video obtained by the Turkish newspaper Hurriyet and made available on Oct. 9, 2018 claims to show Saudi journalist Jamal Khashoggi entering the Saudi consulate in Istanbul, Oct. 2, 2018.
Khashoggi has written articles in The Washington Post that were critical of the Saudi regime and its intervention in the war in Yemen. Cengiz, his fiancee, wrote in the newspaper Tuesday that Khashoggi had been 'somewhat concerned that he could be in danger' when he first visited the consulate September 28, but after that visit was uneventful, seemed unconcerned when he returned last week to pick up the documents they needed to get married.
She called on Trump to 'help shed light' on the journalist's disappearance. She also urged Saudi Arabia's leaders to release security camera video from the consulate area.
Turkish media Wednesday showed what it said was a team of the 15 Saudis arriving at the Istanbul airport on the same day Khashoggi went missing. The Sabah newspaper, which is close to President Recep Tayyip Erdogan, published names and pictures of the Saudi nationals, apparently taken at a passport control station.
Later, eight of the men checked into the Movenpick hotel near the consulate, with seven others checking into a nearby hotel, the Wyndham. Nearly two hours after Khashoggi entered the consulate, video shows two vehicles with diplomatic plates leaving the consulate through police barricades and headed to the Saudi consul general's residence. The 15 Saudis left Turkey at four different times, the Sabah report said.
Washington Post publisher Fred Ryan issued the newspaper's latest plea for information Tuesday, saying neither Saudi Arabia nor Turkey has provided satisfactory answers.
'Silence, denials and delays are not acceptable. We demand to know the truth,' Ryan said in a statement.
Turkey's Foreign Ministry said Tuesday authorities would search the Saudi consulate, but there have been no details about when such a search would take place.
Erdogan said Saudi officials need to prove that Khashoggi left the building.
'We have to get an outcome from this investigation as soon as possible. The consulate officials cannot save themselves by simply saying, 'He has left,'' Erdogan said earlier in the week.
Crown Prince Salman said last week that Riyadh was 'ready to welcome the Turkish government to go and search our premises,' because it had 'nothing to hide' about the missing journalist.
Michael Bowman contributed to this report.