President Donald Trump called on his NATO allies to spend more on defense to fight terrorism.

Trump has said it is not fair for U.S. taxpayers that few NATO members respect the 2 percent of gross domestic product contribution and argued the threshold is not enough to fight terrorism.

"Over the last eight years, the United States spent more on defense than all NATO countries combined. If all NATO members had spent just 2 percent of GDP on defense last year, we would have had another $119 billion for our collective defense," Trump said as leaders arrived in Brussels for a NATO summit.

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

Thursday's NATO meeting, the first for Trump, took place at the new headquarters of the defense alliance.

"I never asked once what the new NATO headquarters cost. I refuse to do that. But it is beautiful," Trump said.

The new building cost 1.12 billion euros ($1.26 billion), according to a NATO fact sheet.

Trump said the U.S. would not "forsake the friends," but he did not explicitly mention and endorse "Article 5," the mutual assistance clause in the NATO charter that he was widely expected to back publicly for the first time.

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