Washington: Saudi Arabia has started a full investigation into the case of journalist Jamal Khashoggi, who was last seen entering the Saudi consulate in Istanbul, US President Donald Trump has said and insisted that blaming Riyadh over his disappearance was premature.

Soon after talking with Saudi Crown Prince Mohammed bin Salman over the phone on Tuesday, Trump in a tweet said that answers related to Khashoggi's disappearance would be forthcoming shortly.

"Just spoke with the Crown Prince of Saudi Arabia who totally denied any knowledge of what took place in their Turkish consulate, Trump said.

Bin Salman was with Secretary of State Mike Pompeo in Saudi Arabia during that call.

In a statement, Pompeo said he "had direct and candid conversations" with the king and the crown prince, as well as Saudi Foreign Minister Adel al-Jubeir.

Trump tweeted that the Saudi Crown Prince "told me that he has already started, and will rapidly expand, a full and complete investigation into this matter. Answers will be forthcoming shortly."

Khashoggi, a dissident Saudi journalist, who wrote for The Washington Post and lived in the US as legal permanent resident was last seen entering the Saudi consulate in Istanbul. Turkish investigative agencies have said that he was brutally killed inside the consulate. They claim to have audio and video evidence of it.

So far Saudi Arabia has denied the allegations and said that Khashoggi left the consulate. Some US media reports said that Saudi Arabia is planning to come out with a report in which it is expected to say that the interrogation of Khashoggi went wrong and was killed in the process.

Trump, under tremendous pressure from lawmakers, has warned of severe punishment. However, he has pushed back again any effort to cancel the mega USD 110 billion arms deal with Saudi Arabia asserting that such a move will hurt US economy and jobs.

"Here we go again with you're guilty until proven innocent," Trump told The Associated Press as he compared the allegations against Saudi Arabia to the sexual misconduct allegations from multiple women against Supreme Court Justice Brett Kavanaugh during his confirmation hearing.

Trump also said "that would be bad" if Saudi Arabia's king and crown prince knew about the suspected killing of Khashoggi in the Saudi consulate.

NBC News reported that the Saudis are discussing issuing an explanation that would admit that Khashoggi was killed in the consulate while giving bin Salman so-called plausible deniability by saying he neither ordered the murder nor knew about it.

It also said that a person with knowledge of the discussions said the kingdom will claim that rogue operatives killed the journalist during either an interrogation or an attempt to kidnap him and return him to his native Saudi Arabia.

Khashoggi had penned articles critical of the country's rulers.

Earlier on Tuesday, Trump said that "I have no financial interests in Saudi Arabia" but in fact he has boasted in the past that "I make a lot of money with them."

Trump's attempt to distance himself from profiting from Saudi Arabia is undercut by a long record showing deals his companies made with that country's government and citizens, media reports said.