U.S. President Donald Trump repeated 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.

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Trump has made similar statements about close allies South Korea and Japan - remarks which have roiled international observers and many pro-Israel advocates concerned about U.S. support for its close allies.

"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.

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.

OPEC's leader Saudi Arabia and its biggest oil-producer ally outside the group, Russia, ruled out in late September any immediate, additional increase in crude output, effectively rebuffing Donald Trump's calls for action to cool the market.

"I do not influence prices," Saudi Energy Minister Khalid al-Falih told reporters as OPEC and non-OPEC energy ministers gathered in Algiers for a meeting that ended with no formal recommendation for any additional supply boost.

Benchmark Brent oil reached $80 a barrel this month, prompting Trump to reiterate on Thursday his demand that the Organization of the Petroleum Exporting Countries lower prices.

The price rally mainly stemmed from a decline in oil exports from OPEC member Iran due to fresh U.S. sanctions.

"We protect the countries of the Middle East, they would not be safe for very long without us, and yet they continue to push for higher and higher oil prices! We will remember. The OPEC monopoly must get prices down now!" Trump wrote on Twitter.

A good relationship

Trump made Saudi Arabia his first stop on his maiden international trip as president last year.

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."

"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.

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.