The President's defence chief Jim 'Mad Dog' Mattis issued the warning during a tense meeting in Brussels earlier today.
He insisted the United States would pay its fair share of money into the transatlantic alliance's budget.
But he added: "If your nations do not want to see America moderate its commitment, each of your capitals needs to show support for our common defence."
Mr Mattis added: "No longer can the American taxpayer carry a disproportionate share of the defence of Western values.
"Americans cannot care more for your children's future security than you do."
President Trump has previously branded Nato "obsolete", sparking fears his administration could quit the alliance.
Donald Trump's defence chief issued the treat to Nato during talks in Brussels Being President Trump: Key Moments Fri, February 3, 2017
Inside Donald Trump's first week in the White House.
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Trump signs an order to review the Dodd-Frank Wall Street to roll back financial regulations of the Obama era.
As President Trump has stated, he had strong support for NATO
But Mr Mattis reaffirmed the US' commitment to the alliance while speaking to reporters in the Belgian capital.
He told reporters: "The alliance remains a fundamental bedrock for the United States and for all the transatlantic community.
"As President Trump has stated, he had strong support for NATO."
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