U.S. President Donald Trump is ramping up the rhetoric against Saudi Arabia’s King Salman, saying he “might not be there for two weeks” without the backing of the United States’ military as OPEC oil prices continue to rise.

Crude oil prices are at a four-year high, and Saudi Arabia is the the world’s largest oil exporter and a leader of OPEC, the Organization of Petroleum Exporting Countries.

“We protect Saudi Arabia — would you say they’re rich?” Trump asked a cheering crowd during a campaign rally Tuesday night in Mississippi. “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, you have to pay.'”

The message to the United States’ most important ally in the Middle East came as analysts warn oil prices could reach $100 a barrel as world production declines and sanctions on Iran go into effect in early November.

Trump and King Salman last spoke via telephone Saturday, discussing “efforts to maintain supplies to ensure the stability of the oil market and ensure the growth of the global economy,” according to the state-run Saudi Press Agency.

Benchmark Brent crude oil is trading near $85 a barrel, the highest rate in four years, as gas prices continue to rise in the United States ahead of the November midterm elections. The average price per gallon is $2.88, up more than 30 cents from a year ago, according to AAA.

Trump also hit global oil producers in a speech to the U.N. General Assembly last week.

“OPEC 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.”

The Associated Press contributed to this report.