President Donald Trump says Germany owes "vast sums of money" to NATO and the U.S. "must be paid more" for providing defense.
But he reiterated his stance that Germany needs to meet its end of the bargain if it is to continue benefiting from the military alliance.
Trump wrote, "Despite what you have heard from the FAKE NEWS, I had a GREAT meeting with German Chancellor Angela Merkel."
He added, "Nevertheless, Germany owes ... vast sums of money to NATO & the United States must be paid more for the powerful, and very expensive, defense it provides to Germany!"
In a joint press conference with Merkel, Trump had said it was "very unfair to the United States" for European allies to take advantage of US defense spending.
"These nations must pay what they owe," he said Friday.
Trump had also thanked Merkel for Germany's commitment of increasing its NATO contributions to two percent of gross domestic product.
At the White House, Merkel said she and Trump discussed Berlin's contributions to NATO and the continuing German military participation in Afghanistan.
The right-wing populist Trump has set a pattern of firing off inflammatory messages on Twitter, particularly on weekends, since taking office January 20.