Story highlights "I hope we will all be able to come together," Antonio Guterres says

He served 10 years as the head of the UN's refugee agency

United Nations (CNN) Antonio Guterres cheerfully walked into the United Nations on Tuesday to officially assume his position as secretary-general.

But looming large over his future is a man not far away, at Trump Tower in Manhattan, who also starts his new job soon.

President-elect Donald Trump has criticized the UN for its failure to perform and for a Security Council vote against Israel on settlements. He even tweeted that the UN was just a place "to talk and have a good time."

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When asked if Trump's criticism worried him, Guterres responded, "No. I am concerned about all the terrible problems we face in the world, all the wars that are happening everywhere." He added, "I hope we will all be able to come together."

Trump did say the UN has "such great potential."

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