"I think every discussion in Europe making sure that collectively the nuclear deterrence is even stronger, fine, but nobody is arguing in Europe to do this as a sort of replacement of the nuclear umbrella of the United States," the NATO secretary general told journalists at the Munich Security Conference.

"Everybody realizes that is the ultimate guarantor -- and all these other discussions are in addition."

German Chancellor Friedrich Merz on Friday told the gathering of Western leaders that he had "held confidential talks with the French president about European nuclear deterrence".

And Prime Minister Keir Starmer of Britain, Europe's other nuclear power along with France, said it was "enhancing our nuclear cooperation with France".

The growing debate over whether to bolster nuclear arsenals on the continent comes as fears grow over the threat from Russia and the reliability of US security commitments under President Donald Trump.

Officials from Trump's administration have told Europe allies to take charge of their conventional defence, but say the US will continue to provide its nuclear cover.