Ties between Turkey and Saudi Arabia have been tense over regional political differences, although the kingdom is a major investor in the Turkish economy. The Washington Post contributor vanished last week while visiting the Saudi Consulate in Istanbul.
The president added that he would invite Khashoggi's fiancee, Hatice Cengiz, to the White House to meet him, after she called for Trump to get involved in the matter. According to the New York Times, officials in Istanbul believe he was killed on orders from the royal court of Saudi Arabia.
Khashoggi feared for his safety before he entered the Saudi diplomatic compound, and asked her to speak to leading Turkish officials if he did not come out of the consulate. He also said the USA was working "very closely" with Turkey, "and I think we'll get to the bottom of it". A spokesman for the State Department insisted the US government had "no advance warning" of Khashoggi's disappearance.
"We are very disappointed to see what's going on".
'And we can not let this happen.
Turkish President Tayyip Erdogan said his country was anxious about Khashoggi's disappearance and can not remain silent, in comments quoted by Hurriyet newspaper on Thursday.
Trump said Wednesday night in an interview on Fox News that "so far it's looking a little bit like" the Saudis are behind the disappearance of Khashoggi, but said "I do hate to commit to what recourse we would take".
The Post, citing anonymous USA officials familiar with the intelligence, said Saudi Crown Prince Mohammed bin Salman ordered an operation to lure Khashoggi from his home in Virginia to Saudi Arabia and then detain him. Media also reported the possibility Mr Khashoggi was taken aboard one of the private planes.
Rubio said on "America's Newsroom" that if evidence of Saudi involvement is found, there will be an effort in Washington, D.C.to "fundamentally alter" the U.S. -Saudi relationship.
White House press secretary Sarah Huckabee Sanders said national security adviser John Bolton and presidential senior adviser Jared Kushner spoke Tuesday to Crown Prince Mohammed about Khashoggi.
While the crown prince has been praised for modernizing some aspects of Saudi life, he has also been ruthless against his critics or anyone standing in the way of his rise to power. Saudi Arabia denies this.
Secretary of State Mike Pompeo then had a follow-up call with the crown prince to reiterate the U.S. request for information and a thorough, transparent investigation. But it's a very serious situation, and it's something we're taking very seriously.
"Well, I think that would be hurting us".
Trump said he had talked "more than once" and "at the highest levels" to partners in Saudi Arabia, which is one of Washington's closest allies and a key market for the United States weapons industry.
"It points to the idea that whatever has happened to him, the Saudis - I mean, they've got some explaining to do", Corker said in a Daily Beast report. They haven't searched the consulate yet, as they have promised to do.
In remarkably measured statements that made no mention of the murder claim, President Recep Tayyip Erdogan has expressed hope that Khashoggi would turn up alive and urged Riyadh to prove the journalist left the consulate.
A total of 25 to 30 professional and non-professional journalists are now believed to be detained in Saudi Arabia, which is ranked 169th out of 180 countries in RSF's 2018 World Press Freedom Index, the organisation also said.
"The Yemen war is a proxy war with Iran", Graham said, adding that Yemen and Khashoggi are "two different things", a sentiment echoed by other Republicans.