U.S. President Donald Trump said he would back the sale of American-made F-35 fighter jets to Saudi Arabia, a day before the crown prince arrives in Washington.

"We will be doing that. We will be selling F-35s," Trump told reporters when asked if Washington would agree to sell Riyadh the jets at Tuesday's meeting. "They've been a great ally," he added.

Trump is to meet Saudi Crown Prince Mohammed bin Salman at the White House on Tuesday. The official, speaking to Reuters on condition of anonymity, said Trump's support is likely and the president "wants to talk to the crown prince about it tomorrow, and then we'll make a determination."