President Macron has aired the idea that France's deterrence force could be used to defend of other European countries.

European leaders showed a cautiously receptive ear to President Emmanuel Macron's proposal to debate extending the French nuclear umbrella to Europe on Thursday, though some were reluctant to draw a line under years of U.

"In the current situation, the French and British nuclear forces are a complement to U.S. extended deterrence, but they would not constitute a viable solution in the event of an abrupt withdrawal of U.S. nuclear forces," the Washington-based Centre for Strategic & International Studies said.