European leaders have called for greater unity and military cooperation across the continent in response to comments from Donald Trump that threatened to undermine the basis of Nato.

Donald Tusk, Poland’s prime minister, said on a visit to Paris on Monday that there was “no alternative” to the EU and the transatlantic alliance before a summit in which he discussed deepening defence relationships with the French president, Emmanuel Macron.

“It is probably here in Paris that the words from The Three Musketeers by Alexandre Dumas resonate most clearly: ‘All for one, and one for all,’” said Tusk, in a thinly veiled riposte to the former US president and frontrunner for the Republican presidential nomination.

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