Defense Secretary James Mattis issued a warning Feb. 15 to allies in the North Atlantic Treaty Organization (NATO) to increase military spending.
The retired general was speaking at a meeting of NATO defense ministers in Brussels, Belgium, according to Reuters.
"No longer can the American taxpayer carry a disproportionate share of the defense of Western values," Mattis said, according to Politico. "Americans cannot care more for your children's future security than you do."
He also noted that America had been pushing for higher defense spending for many years, referring to statements made by former Defense Secretary Robert Gates.
"The impatience Mr. Gates predicted is now a governmental reality," added Mattis.
President Donald Trump stated during the election campaign that NATO as an alliance was "obsolete" and called on its other members to hike military spending. The United States is urging each member to spend a minimum of 2 percent of economic output on defense.
"Disregard for military readiness demonstrates a lack of respect for ourselves, for the alliance and for the freedoms we inherited which are now clearly threatened. America will meet its responsibilities, but if your nations do not want to see America moderate its commitment to this alliance, each of your capitals needs to show support for our common defense," added Mattis.
As Mattis spoke in Brussels, 120 American troops deployed to Bulgaria as part of a NATO mission aimed at proving to Russia that Washington supports its allies. Armored vehicles will arrive by the end of the week to participate in operation Atlantic Resolve, Reuters reported.
Some 2,700 American troops arrived in Poland in January for joint operations. Russia responded by saying it felt threatened.
At the NATO meeting, Mattis mentioned Russia's annexation of Crimea and intervention in Ukraine in 2014.
"The events of 2014 were sobering and we must continue to adapt to what's being revealed to us in terms of our security challenges," he said, Politico reported.
Despite his earlier criticisms, Mattis emphasized the Trump administration's continued commitment to NATO.
"The alliance remains a fundamental bedrock for the United States and for all the transatlantic community, bonded as we are together," added Mattis. "As President Trump has stated, he has strong support for NATO."