France has warned Germany that it could trigger a nuclear conflict with Russia if it does not define how it would use its newly acquired long-range missiles, the Financial Times reported.

Berlin is acquiring and developing ground-launched missiles with ranges varying from 500 kilometres to more than 2,000 kilometres, as part of a wider European effort to bolster defences and deter Moscow from any attacks on Europe. But French and German officials are set to hold talks on how the weapons will be used, amid fears that their use could trigger a "nuclear response" from Russia. The confusion centres on the definition of deep precision strikes.

"If the Russians don't get the signal right you could get to the nuclear threshold without realising," one French official told the Financial Times. An attack on a Russian target with a conventional weapon could draw a far greater response from Russia if the signalling is not interpreted correctly.

The warning carries a knock-on effect for France because of President Emmanuel Macron's "forward deterrence" policy, under which Moscow could hold Paris accountable for strikes carried out by its partners. "If you invite someone into your house, you are responsible if they set it ablaze," said one official with knowledge of the discussions.

Six people familiar with the talks told the Financial Times that French officials are hoping to reach an agreement on how both countries could better align their defence programmes in light of the risk. "There are habits we developed over time. The Germans do not have it," said one source. "It would be much better to have a clear and pretty public doctrine so that the Russians never get a signal wrong or misunderstand."

A senior German official said Berlin agreed that European capitals needed "a joint doctrine and a joint understanding about the escalation ladder" and "could not agree more" with the assessment. A British official felt the fears may be overestimated at the present moment, saying "Germany's strategic culture is evolving very quickly" and "we absolutely believe we should embrace that, not cling to the past stereotypes." Germany's defence budget stands at 780 billion euros over the five-year period until 2030. It follows reports earlier this year that Germany is in talks to fund Britain's Trident programme in an attempt to bolster Europe's nuclear deterrent in any war against Putin.