Switzerland is not a member of NATO and has a long-standing policy of neutrality on the world stage.

Mr Biden’s mistake was immediately mocked by the Republican National Committee.

The president has made a number of verbal mistakes on the world stage, such as Taiwan, some of which have raised questions about an abrupt change in US foreign policy, only for the White House to return to the comments.

Mistakes have led Mr Biden’s opponents to suggest that the 79-year-old is unfit to be the leader of the free world.

Mr Biden’s presence at the three-day NATO summit in Madrid was designed to strengthen the unity of the alliance, which had been slandered under his predecessor, Donald Trump.

“I think we can all agree that this has been a historic NATO summit,” Biden said as he spoke to reporters at a closing news conference.

“This summit was about strengthening our alliances, meeting the challenges of our world as it is one day and the threats we will face in the future,” Biden said.

The most important achievement of the three-day event was to reach an agreement between Turkey, Finland and Sweden to pave the way for the Nordic nations’ accession to NATO.

Mr Biden told reporters on Thursday: “Putin wanted NATO ‘Finlandisation’. He got the NATOisation of Finland”.