French naval personnel have boarded a Russia-linked oil tanker suspected of being used to launch drone flights that disrupted airports in Denmark last month.

The vessel, identified as the Boracay and long associated with Russia’s so-called ‘shadow fleet’, was intercepted on Sunday while carrying 750,000 barrels of crude oil from Primorsk, near St Petersburg, to Vadinar in India.

It was diverted to Saint-Nazaire in western France for investigation after prosecutors in Brest opened a case into its “failure to justify the nationality of the vessel” and its “refusal to cooperate”.

The French president, Emmanuel Macron, welcomed the move, calling the probe a “good thing”. The Kremlin, meanwhile, said it had no information about the tanker.

The Boracay has repeatedly changed names and registrations, sailing under its previous name Pushpa around Denmark during the 22 and 24 September drone sightings that forced the temporary closure of Copenhagen and Aalborg airports.

Experts have suggested large fixed-wing drones may have been launched from ships near Danish waters, though responsibility has not been confirmed.

Danish media have also pointed to two other commercial ships, the Astrol-1 and Oslo Carrier-3 and filmed the Russian warship Aleksandr Shabalin near Langeland in the Baltic.

German officials reported similar incursions over Schleswig-Holstein, with reconnaissance drones flying over military and infrastructure sites.

Danish prime minister Mette Frederiksen described the incidents as part of a “hybrid war”, saying: “From a European perspective, there is only one country that is willing to threaten us, and it is Russia.”

The EU will address the threat at a summit in Copenhagen on Thursday, where leaders are expected to discuss plans for a joint “drone wall”.

Several European countries, including the UK, have already deployed anti-drone systems to Denmark.

The Boracay is subject to sanctions from the UK and EU and has been repeatedly cited as part of Russia’s shadow fleet; a network of vessels with murky ownership structures used to transport oil in breach of restrictions.

In April, when operating under yet another name, Kiwala, the tanker was briefly detained in Estonia over registry irregularities before being released.

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