U.S. President Donald Trump made an undiplomatic remark about close ally Saudi Arabia on Tuesday, saying he warned Saudi Arabia's King Salman he would not last in power "for two weeks" without the backing of the U.S. military.

"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.

Trump did not say when he made those remarks to the Saudi monarch.

He has also pressed other U.S. allies, such as Japan, South Korea and Germany, to take more of the financial burden of their defense.

Trump called King Salman on Saturday and they discussed efforts being made to maintain supplies to ensure oil market stability and global economic growth, according to Saudi state news agency SPA.

Saudi Arabia is the world's top oil exporter and the de facto leader of OPEC, which has been criticized by Trump 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."

Trump's harsh comments came after criticizing oil producers in his speech before the U.N. General Assembly last week as the crude oil prices reach a four-year high. "OPEC [Organization of Petroleum Exporting Countries] and OPEC nations are, as usual, ripping off the rest of the world, and I don't like it. Nobody should like it," he said. "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 and they must contribute substantially to military protection from now on."

Trump, facing political pressure at home, has been calling on OPEC and American allies like Saudi Arabia to boost their production to lower global crude oil prices. However, analysts are warning prices could go up to $100 a barrel as the world's production is already stretched and Trump's sanctions on Iran's oil industry take effect in early November. Trump in July tweeted without evidence that Saudi Arabia would increase its production "maybe up to 2,000,000 barrels" a day. He accused the OPEC countries of a price "monopoly" as they are "doing little" to help ease the prices increase. Saudi Arabia currently produces some 10 million barrels of crude oil a day. Its record is 10.72 million barrels a day.

Despite the harsh words, the Trump administration has had a close relationship with Saudi Arabia, which it views as a bulwark against Iran's ambitions in the region. Saudi Arabia is one of the major buyers of U.S.-made weaponry, and the U.S. provides intelligence and aerial refueling support to Saudi-led coalition fighting rebels in Yemen.

Riyadh has worked to cultivate warm relations with Trump after having rocky moments with former President Barack Obama. Saudi Arabia welcomed Trump for his first overseas trip as president. Trump's administration, particularly his son-in-law Jared Kushner, has sought a close relationship with King Salman's son and Mohammed bin Salman, the countrytarget="_blank"'>