The US president issued his firmest statement yet over the disappearance of Washington Post contributor Jamal Khashoggi.
The Saudi dissent vanished after entering the Gulf kingdoms consulate in Istanbul, Turkey 12 days ago.
Turkish sources claim he was killed by a hit squad of Saudi agents.
Interior Minister Prince Abdulaziz bin Saud bin Naif bin Abdulaziz denies the claims.
Mr Trump indicated earlier this week he was reluctant to pull out of a multi-billion-dollar US weapons deal with the Saudis to show White House anger if the missing journalist was killed by the Saudis.
But speaking to 60 minutes on Saturday, he warned the US would be very upset and angry if the Saudis ordered Mr Khashoggis killing.
Mr Trump said: Theres a lot at stake. And, maybe especially so because this man was a reporter.
Theres something, youll be surprised to hear me say that, theres something really terrible and disgusting about that if that was the case.
Were gong to get to the bottom of it and there will be severe punishment.
He added: Its being investigated, its being looked at very, very strongly.
As of this moment they deny it, and they deny it vehemently. Could it be them? Yes.
Mr Khashoggis disappearance sparked international comdemnation.
UK foreign secretary Jeremy Hunt told Saudi Arabia Britain wants urgent answers over the reporters disappearance.
Former foreign secretary Malcolm Rifkind called on Britain to impose sanctions on Saudi Arabia.
But despite Mr Trump firing a warning shot at the Saudis, he underlined the White House would protect key defence deals.
When asked if he would impose sanctions on the Saudis, he said it depends on what the sanction is.
Mr Trump said: They are ordering military equipment.
Everybody in the world wanted that order. Russia wanted it, China wanted it, we wanted it.
We got it. And we got all of it. Every bit of it. I tell you want I dont want to do Boeing, Lockeed, Raytheon, all those I dont wanna hurt jobs. I dont want to lose an order like that.
There are other ways of punishing to use a word thats a pretty harsh word, but its true.