President Trump, right, beside NATO Secretary-General Jens Stoltenberg at the start of the NATO summit at its new headquarters in Brussels, May 25, 2017. Reuters/Christine Hartmann

President Donald Trump on Thursday lectured a group of leaders from member countries of the North Atlantic Treaty Organization over not contributing their "fair share" in defense spending.

Standing beside Secretary-General Jens Stoltenberg at NATO headquarters in Brussels, Trump blasted the nearly two-dozen member countries that have not met their "financial obligations" to increase defense spending to 2% of GDP.

"This is not fair to the people and taxpayers of the United States, and many of these nations owe massive amounts of money from past years," Trump said as the other leaders stood in awkward silence.

"We should recognize that with these chronic underpayments and growing threats, even 2% of GDP is insufficient to closing gaps in modernizing readiness and the size of forces. We have to make up for the many years lost," he said.

Trump said that 23 of the 28 NATO members have still not met the 2% commitment, adding that the alliance would have had an additional $119 billion "for our collective defense" last year if the quota had been met.

"If NATO countries made their full and complete contributions, then NATO would be even stronger than it is today, especially from the threat of terrorism," Trump said.

Yet foreign-policy experts have previously said that Trump's characterization of NATO as an organization that member countries "owe" money to is false.

NATO leaders decided in 2011 that each country would boost defense spending to 2% of the national GDP by 2024, but the spending goes toward the countries' own militaries and is not considered a payment to NATO.

Some NATO leaders, such as Canadian Prime Minister Justin Trudeau, have sought to skirt the 2% quota by arguing that "there are many ways of evaluating one's contribution to NATO" besides increasing defense spending.

Watch Trump's remarks below: