At a press conference marking the end of the NATO summit in Madrid, the US president recounted the behind-the-scenes talks putting militarily non-aligned Finland and Sweden on track to join the Western alliance in a major rebuff to Russia.

Except he misspoke, saying there was a plan to call the leader of famously neutral Switzerland about joining.

Quickly realizing his stumble, Biden said: "Switzerland, my goodness."

"I'm getting really anxious here about expanding NATO," he joked, before adding for the record: "Sweden."

Biden, 79, has long been known for his verbal gaffes during a political career spanning half a century.