A top German official has called on the UK and France to do more to protect Europe from threats.
Finance minister Christian Lindner was speaking amid concerns that Nato may no longer be able to count on US support should Donald Trump return to the White House.
Britain and France are Europe's only nuclear powers and despite the fact that both are a part of Nato, both maintain their own independent control over their respective nuclear arsenals.
The collective power between London and Paris is a fraction of that employed by Russia, which has the largest supply of weapons in the world.
French Finance Minister Christian Lindner has criticised the former President's comments
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Writing in German newspaper Frankfurter Allgemeine Zeitung, Lindner said: "We should understand Donald Trump's recent statements as a call to further rethink this element of European security under the umbrella of NATO.
"The strategic nuclear forces of France and Great Britain are already making a contribution to the security of our alliance.
"The question is: under what political and financial conditions would Paris and London be prepared to maintain or expand their own strategic capabilities for collective security?
"When it comes to peace and freedom in Europe, we must not shy away from these difficult questions."
German Federal Finance Minister Christian Lindner
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Nato's nuclear deterrence relies massively on the US, which has the second largest stockpile of nukes at around 5,200 to Russia's 5,800 - though more a thousand of them are thought to be retired and awaiting disarmament.
It comes as US intelligence sources claimed the Kremlin is developing plans to deploy anti-satellite missile technology into space. This info is prompting alarm from American lawmakers who called on the Biden administration to urgently declassify the details of the alleged programme.
German Defence Minister Boris Pistorius dismissed the comments from the finance minister. Speaking to reporters in Brussels, he said: "The nuclear debate is really the last thing we need at the moment. It is an escalation in the discussion that we don't need."
Vice chancellor Robert Habeck added: "The last thing the French want is European co-management over their army."
German Defence Minister Boris Pistorius has dismissed his colleague's comments
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Meanwhile, Russian President Vladimir Putin said in an interview broadcast on Wednesday that he preferred Joe Biden to Donald Trump but was willing to work with any US president.
Putin was asked by interviewer Pavel Zarubin who was "better for us" out of Biden or Trump.
He replied: "Biden. He is a more experienced, predictable person, a politician of the old school. But we will work with any US president who the American people have confidence in."