COPENHAGEN, Oct 1, 2025 (BSS/AFP) - France is probing an EU-sanctioned, Russian-linked oil tanker for "serious offences", President Emmanuel Macron said Wednesday -- stopping short of confirming reports of a connection to mysterious drone flights in Denmark.

French authorities have opened a probe into the Boracay, a Benin-flagged vessel anchored off France's Atlantic Coast that has been blacklisted by the European Union for being part of Russia's sanction-busting "shadow fleet".

"There were some very serious offences committed by this crew, which justify the current judicial procedure," Macron told reporters at an EU leaders' summit in Copenhagen.

Built in 2007 and variously known as Pushpa and Kiwala, the Boracay has been anchored off Saint-Nazaire in western France for several days.

According to the specialist website The Maritime Executive, the vessel is suspected of being involved in mystery drone flights that disrupted air traffic in Denmark in September.

The publication said the tanker and other ships could have been used either as launch platforms or as decoys.

But when asked about those claims, Macron said he would "remain very careful", as it was not for him to establish a link between the Boracay and the drone flights.

The French operation however underscored the importance of European efforts to stop the "shadow fleet" of vessels aiding Russia to circumvent Western sanctions.

The European Union has sanctioned hundreds of ageing tankers used by Russia to circumvent oil export curbs imposed after the 2022 invasion of Ukraine to sap Moscow's war chest.

Among them is the Boracay, which was blacklisted in February under the name Kiwala.

The public prosecutor's office in the northwestern French city of Brest said it had opened an investigation following a report from the navy.

The probe was launched over the crew's "failure to justify the nationality of the vessel" and "refusal to cooperate", Brest public prosecutor Stephane Kellenberger told AFP.

The tanker left the Russian port of Primorsk outside Saint Petersburg on September 20 and was due to arrive in Vadinar in northwestern India on October 20, according to data from the Marine Traffic tracking website.