President Donald Trump on Wednesday said he was "very upset with NATO" because the United States pays "billions and billions of dollars too much" to protect the alliance's member countries, while arguing that America's allies have not done enough to support Washington in confronting Iran.

Speaking alongside NATO Secretary General Mark Rutte before a summit meeting in Ankara, Turkey, Trump renewed his long-standing criticism that European allies have relied too heavily on U.S. military protection while failing to shoulder a fair share of the financial burden.

"We've been treated unfairly," Trump said. "We pay disproportionately.

"I'm very upset with NATO that we pay far, far too much, billions and billions of dollars too much because it's unfair because we're protecting them. So we protect them, but they're not there for us."

Trump said he was especially frustrated that several NATO members declined to provide greater assistance during recent U.S. military operations against Iran, which he described as the world's leading state sponsor of terrorism.

The president said he personally contacted leaders of Germany, France, Britain, and Italy seeking additional cooperation but was disappointed by their responses.

He singled out Spain for particularly sharp criticism, calling it "a terrible partner in NATO" and suggesting the United States should halt trade with the country because of its defense spending and refusal to support U.S. military operations.

Trump also criticized NATO over Greenland, repeating his contention that the strategically located Arctic territory is vital to U.S. national security and expressing frustration over resistance to American ambitions there.

The president's remarks underscored tensions surrounding this year's NATO summit.

CNN reported Trump arrived in Ankara frustrated over Iran, Greenland, and what he views as years of European allies failing to contribute enough to their own defense while leaving Washington to bear the bulk of the costs.

Despite Trump's criticism, Rutte praised the president for pressuring alliance members to dramatically increase military spending.

Rutte credited Trump with helping secure more than $1.2 trillion in additional defense commitments from Canada and European NATO countries, saying those investments are supporting nearly 200,000 U.S. jobs through purchases from America's defense industry.

He also defended NATO's assistance during recent operations against Iran, noting that thousands of flights departed from European bases in support of the U.S.-led mission and that many allies provided significant logistical support.

Trump acknowledged Rutte's leadership, calling him "a great leader" and NATO's "biggest asset," while maintaining that previous administrations under former Presidents Barack Obama, Joe Biden, and George W. Bush failed to force allies to pay more for their own defense.

"You did what [former President Dwight D.] Eisenhower started trying to do," Rutte told Trump. "It's your win."