Defense Secretary James Mattis on Friday said that NATO has President Trump's "full support" as he sought to reassure allies about the future of the transatlantic security alliance.

“President Trump came into office and has thrown now his full support to NATO,” Mattis said during his opening remarks at the Munich Security Conference before hundreds of security experts and policymakers from around the world. “He too espouses NATO’s need to adapt to today’s strategic situation for it to remain credible, capable and relevant.”

But Mattis also stressed to allies that the new administration expects them to boost defense spending and share more of the burden.

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“It is a fair demand that all who benefit from the best alliance in the world carry their proportionate share of the necessary costs to defend our freedoms,” he said.

Mattis is on his first trip to Europe as Pentagon chief, a visit that's seen him work to mend relations with allies worried about Trump's stance on NATO.

During the campaign, in a July interview with The New York Times, Trump suggested that the U.S might not come to the aid of some NATO allies if they were attacked if he believed they had not been contributing their fair share.

And in a January interview with Germany’s Bild newspaper, Trump called NATO “obsolete” and criticized its counter-terrorism efforts.

The Pentagon chief, though, dropped any suggestion that the U.S. might not back its allies.

On Friday, he insisted the U.S. was committed to Europe's security.

“American security is permanently tied to the security of Europe,” he said before hundreds of security experts and policymakers from around the world.

Last week, German Defense Minister Ursula von der Leyen called requests for increased funding “a fair demand” following her first meeting with Mattis.

In his remarks, Mattis also highlighted Europe's Baltic nations, who are increasingly fearful of Russia.

“Unified by these growing threats to our democracies, we possess strong resolve. We are going to adapt the alliance,” Mattis said.

Mattis has taken a tougher tone toward Russia than Trump, who has downplayed Russian hacking in the 2016 election and vowed to improve relations with Russian President Vladimir Putin.

On Thursday, Mattis said there was "little doubt" Russia had tried to meddle in U.S. politics.

The Munich Security Conference is an annual meeting for worldwide leaders and experts to address security issues. Sen. John McCain John Sidney McCainThe electoral reality that the media ignores Kelly's lead widens to 10 points in Arizona Senate race: poll COVID response shows a way forward on private gun sale checks MORE (R-Ariz.) also spoke Friday, and Vice President Pence will address the conference on Saturday.