"We protect Saudi Arabia. Would you say they're rich. And I love the King, King Salman. But I said 'King — we're protecting you — you might not be there for two weeks without us — you have to pay for your military,'" Trump said to cheers at a rally in Southaven, Mississippi on Tuesday.
Trump, however, did not say when he made such remarks to the Saudi monarch.
This comes a few days after the Republican president called on Riyadh to increase its military spending, with an eye on more weapons sales to the "rich" kingdom.
"I love Saudi Arabia. They are great, King Salman, I spoke with him this morning. I said, king, you have got trillions of dollars. Without us, who knows what’s going to happen. .... With us they are totally safe. But we don’t get what we should be getting," he said at a rally in West Virginia on Saturday.
Despite the harsh rhetoric, the Trump administration has maintained a close relationship with Saudi Arabia, which it sees as a bulwark against Iran’s rising influence in the region.
Last year, Trump signed the largest arms deal in history with the country despite warnings that he could be accused of being complicit in the regime's war crimes in Yemen.
Trump flew to Saudi Arabia as his first stop on his maiden international trip as president in 2017, during which Saudi Arabia agreed to buy $110 billion worth of US weapons and signed "investment" deals worth billions more.
Analysts say Trump is milking wealthy Persian Gulf Arab countries and exploiting conflicts in the Middle East to boost US arms sales to the oil-rich states.
Saudi Arabia is the world's top oil exporter and the de facto leader of OPEC, which Trump has criticized for high oil prices.
Speaking at the United Nations General Assembly in New York last month, Trump said OPEC members were "as usual ripping off the rest of the world."
"We defend many of these nations for nothing, and then they take advantage of us by giving us high oil prices. Not good. We want them to stop raising prices, we want them to start lowering prices," Trump said.
Trump called King Salman on Saturday to discuss “stability of the oil market” as well as “developments in the Middle East region and the world,” according to Saudi state news agency SPA.