In a statement by his spokesman, Mr Stephane Dujarric, on Monday, Gurerres also congratulated the President-elect Joe Biden and the Vice President-elect Kamala Harris.
He said the partnership between the U.S. and the UN “is an essential pillar of the international cooperation needed to address the dramatic challenges facing the world today”.
The UN was created after World War II at the instance of the U.S., which provides the largest financial contribution to the organisation’s overal budget.
But the partnership has strained by the “America First” foreign policy of the President Donald Trump administration.
Trump broke away from his predecessors’ support for multilateralism and the Rules Based International Order (RBIO) represented by the UN.
Since 2016, the president hardly misses any opportunity to deride the organisation, which he once described as a “club for people to get together, talk and have a good time”.
In a speech at a 2016 meeting of the American-Israel Public Affairs Committee, Trump assailed the “utter weakness and incompetence of the United Nations”.
He has also complained about the cost to the United States of helping to fund the 193-nation body.
The Trump administration is in the process of withdrawing the U.S. from the World Health Organisation (WHO), a UN Agency, over alleged control by China.