U.S. President Donald Trump warned Saudi Arabia would be unlikely to last a fortnight without military assistance from Washington.

"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. "You have to pay."

Trump made the remarks about the close U.S. ally during a campaign rally in Mississippi on Tuesday, drawing applause from supporters.

The president did not specify when he made the remarks, but was likely referring to a weekend call with King Salman bin Abdulaziz al-Saud.

That call focused on "issues of regional concern," according to the White House.

Trump has pressured OPEC to lower crude oil prices as the cost recently increased above $80 per for Brent. Saudi Arabia plays a critical role in the oil cartel.

In addition to lowering oil prices, Trump has called on close U.S. allies to shoulder more of the cost of defense spending, but Tuesday warning marked the most serious criticism of Riyadh.