President Donald Trump talks with reporters in the Oval Office of the White House, in Washington. Picture: Evan Vucci/AP

Washington - US President Donald Trump promised "severe punishment" for Saudi Arabia if the kingdom's leadership was behind the disappearance of journalist Jamal Khashoggi.

"We are going to get to the bottom of it and there will be severe punishment," Trump told the CBS News programme "60 Minutes."

When Trump was asked if Khashoggi, a Saudi dissident, was murdered on the government's order, he replied: "It's being investigated, it's being looked at very, very strongly, and we would be very upset and angry if that were the case."

"As of this moment, they deny it, and they deny it vehemently. Could it be them? Yes."

Trump said he was reluctant to cancel a 110-billion-dollar arms deal with the Saudis.

"I don't want to hurt jobs. I don't want to lose an order like that. And you know what, there are other ways of punishing - to use a word that's a pretty harsh word - but it's true."

An excerpt of the interview, due to air in full on Sunday, was released on Saturday.