German Chancellor Friedrich Merz told the Munich Security Conference (MSC) 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 UK's nuclear deterrent already protects NATO members, and Starmer said "any adversary must know that in a crisis they could be confronted by our combined strength" alongside France.

Still, while the United States and Russia have thousands of nuclear warheads each, the combined French and British arsenal is in the hundreds.

Discussion of nuclear armament has long been viewed as taboo in many other European countries -- but Russian aggression and worries about US commitment have forced the issue into mainstream European politics.

In a report assessing "Europe's nuclear options" published for the MSC, experts warned that the relatively small nuclear arsenals of France and the United Kingdom might not be enough to face down Russia without US support.

"Europeans can no longer outsource their thinking about nuclear deterrence to the United States," the group of 11 experts warn in the paper, which calls on Europe to "urgently confront a new nuclear reality" in the face of "Russia's nuclear-backed revisionism".

Many European officials are convinced that Moscow's territorial ambitions will not be confined to Ukraine, and that other European countries -- including even NATO members -- could face some sort of attack.

US President Donald Trump's disdainful comments about NATO and his highly transactional approach to foreign relations, meanwhile, have Washington's European allies questioning whether they can risk relying on US protection.

- 'Complacency has ended' -

The MSC report lays out five nuclear options for Europe, but cautions that none are good and that there is "no low-cost or risk-free way out of Europe's nuclear predicament".

"The era in which Europe could afford strategic complacency has ended," the authors write.

"However uncomfortable the debate may be, the new security environment requires European policymakers to confront the role of nuclear weapons in the defence of the continent directly and without delay -- and to invest the resources needed to do so competently."

The five options are: Continue to rely on American deterrence; strengthen the role of British and French nuclear weapons in a European deterrent; jointly develop European nuclear weapons as a deterrent; increase the number of European countries with their own nuclear arsenals; or expand European conventional military power to present a more intimidating non-nuclear deterrent.

Sticking with the status quo, and relying on America's unmatched military might, remains "the most credible and feasible option" in the short term, according to the authors.

"We have nuclear deterrence already" within the NATO framework "which is working, which has plans with capabilities and doctrines," Estonian Foreign Minister Margus Tsahkna told AFP.

Merz declared that European NATO allies need to remain united while building up a European nuclear deterrence, stressing that "we will not allow different security zones to emerge in Europe".

- Macron's speech -

The capability gap between the United States and Russia on the one hand, and the much small French and British arsenals on the other, is currently so large that very few believe Europeans can assume full responsibility for deterrence in the short term.

"If there's going to be some kind of bigger European investments in France or the UK's nuclear deterrence, that's only a good thing," Finnish Defence Minister Antti Hakkanen recently told AFP.

But he quickly added: "If you're talking about to compensate US nuclear deterrence, that's not realistic at this point."

Still, experts welcomed the increasingly serious political debate on an issue that has long worried military planners.

"That's very positive, but now we need action," Heloise Fayet of the French Institute of International Relations (Ifri), a contributor to the MSC report, told AFP.

The report notes that both France and Britain would face a range of challenges in growing their arsenals and extending nuclear protection across Europe, from hefty costs to tricky questions about who holds final authority to launch the warheads.

Britain's nuclear weapons also currently depend heavily on US technology, meaning for the moment there is "no sustainable future for a UK nuclear deterrent without US collaboration," the experts note.

French President Emmanuel Macron, who has previously raised the possibility of extending France's nuclear umbrella across Europe, is scheduled to deliver a major speech on French nuclear doctrine at the end of February.

Macron said in Munich he was considering a doctrine that could include "special cooperation, joint exercises, and shared security interests with certain key countries".

"This speech by Macron will be very important," said Fayet. "It has generated enormous expectations in Europe."