"State Department senior officials have spoken with the Kingdom of Saudi Arabia through diplomatic channels about this matter … We call on the government of Saudi Arabia to support a thorough investigation of Mr. Khashoggi's disappearance and to be transparent about the results of that investigation," the statement reads.
According to the Saudi Press Agency, citing the country's Consulate General, the journalist disappeared after he left the diplomatic mission's compound. The Saudi Consulate General also stated that it was cooperating with Turkish authorities to determine the circumstances surrounding the journalist's disappearance.
Meanwhile, US President Donald Trump said Monday he was also troubled by reports about the Saudi journalist's unclear fate.
"I am concerned about it. I don't like hearing about it. And hopefully that will sort itself out. Right now nobody knows anything about it, but there are some pretty bad stories going around. I do not like it," Trump was quoted saying by Reuters at the White House on Monday.
However, a Saudi source at the Istanbul consulate denied that had been killed at the mission, and said that the accusations were wrong. The Saudi consulate also denied that Khashoggi was abducted, Reuters reported.
Khashoggi reportedly left Saudi Arabia last year, claiming that he feared retribution for his criticism of Saudi policy in the Yemen war and the kingdom's crackdown on dissent.