BRUSSELS (AP) — U.S. Vice President Mike Pence on Monday vowed to stand with the European Union and the NATO military alliance, but was met with some skepticism from leaders shaken by President Donald Trump's more critical comments.

European Union Council President Donald Tusk said he had "open and frank talks" with Pence and that the bloc would watch closely to ensure the U.S. acts on its words of support.

"I heard words which are promising for the future, words which explain a lot about the new approach in Washington," Tusk said.

"Too many new and sometimes surprising opinions have been voiced over this time about our relations — and our common security — for us to pretend that everything is as it used to be," he said, adding that Europe was counting on the United States' "wholehearted and unequivocal" support.

Tusk added, "Both Europeans and Americans must simply practice what they preach."

Trump's benevolence toward Russian President Vladimir Putin and campaign rhetoric that included branding NATO obsolete and vowing to undo a series of multinational trade deals has sparked anxiety in Europe. Trump was also supportive of Britain's vote last year to leave the 28-nation EU, a withdrawal known as Brexit. And he has suggested that the EU itself could soon fall apart.

In a visit Brussels, Pence said Trump had asked him "to express the strong commitment of the United States to continued cooperation and partnership with the European Union."

After talks with NATO Secretary General Jens Stoltenberg, Pence reiterated the administration's strong support for the alliance, but warned that Trump wants to see "real progress" by the end of the year on boosting defense spending.

NATO leaders agreed in 2014 that alliance members needed to start spending at least 2 percent of their gross domestic product by 2024. Only five nations currently do so: the United States, Britain, Poland, Estonia and Greece.

"The truth is many others, including some of our largest allies, still lack a clear and credible path to meet this minimum goal," Pence said.

Asked what the administration would do if allies failed to meet the defense spending target, Pence said, "I don't know what the answer is to 'or else,' but I know that the patience of the American people will not endure forever."

Pence's meetings in Brussels were aimed at assuring European leaders that his words reflected the views of Trump and would not easily be swept away at the whim of the U.S. president or undermined by statements issued on Twitter.

Pence, as he did in an address Saturday at the Munich Security Conference, also said Trump would demand that Russia honor its commitments to end the fighting in Ukraine.

"In the interest of peace and in the interest of innocent human lives, we hope and pray that this cease-fire takes hold," he said.

The vice president also noted the "heartbreaking" suicide bombings at the Brussels airport and subway system in March 2016, and said the U.S. would continue to collaborate with EU partners to address safety and combat terrorism.

"The United States' commitment to the European Union is steadfast and enduring," he said.

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