(CNN) President Trump said in his inauguration speech that the slogan "America First" would govern his administration and approach to foreign policy. But UN Secretary-General António Guterres believes that the President's pledge is "detrimental to American interests."

The whole idea of "America first" is predicated on a belief that "the interests of the American people are best protected by the US in itself, and that international organizations do not contribute much to it," Guterres told CNN's Fareed Zakaria on Sunday.

But, the Secretary-General emphasized, this simply "wasn't true."

"The US is too big and too relevant to be able to think it alone. The way things happen in the world has a very important impact in the way things happen in the United States," he said.

As a result, it's important for the United States to operate with a global mindset, Guterres insisted. This in spite of the fact that, in his first year of office, President Trump has pulled out of the Paris Accords, and has announced that he will be withdrawing US membership of UNESCO, the United Nations cultural organization.

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