NATO Secretary General Jens Stoltenberg said that thanks to the US and Britain's atomic weapons, Europe was already protected by a longstanding and effective nuclear umbrella.

While a NATO member, France does not make its atomic weapons available to the alliance, but in a major speech last week Macron called for dialogue among EU countries about what role the French nuclear deterrent could play.

Stoltenberg, who last year clashed with Macron over the French leader's claims NATO was suffering "brain death" in its geopolitical thinking, gave his latest suggestion a frosty reception.

"We have to remember that we have a European nuclear deterrent today -- 28 allies deliver that every day and it's not only a promise, but it's something that has been there for decades," Stoltenberg told reporters at the Munich Security Conference.

"It's tried and tested, we exercise it, and it's institutionalised, and it is the ultimate security guarantee for Europe."

France is the EU's only nuclear power after Brexit and Macron has championed the idea of European "strategic autonomy" -- the ability to defend itself without relying on the US -- though he insists on his commitment to NATO.