PARIS (AP) -- The captain of an oil tanker immobilized off the country's Atlantic coast which President Emmanuel Macron linked to Russia will go on trial in February over the crew's alleged refusal to cooperate, a French prosecutor said Thursday.

Macron has alleged that the tanker belongs to Russia's so-called shadow fleet of aging tankers of uncertain ownership that are avoiding Western sanctions over Moscow's war in Ukraine and didn't rule out that it could have been involved in drone flights over Denmark as it was sailing last week off the coast of the Nordic country.

Asked about whether the tanker could be linked to drones flights, Macron said that "I'm very cautious because our services and our justice are still working ... I don't exclude it at all, but I cannot here attribute very clearly and establish a clear link between these two phenomenon."

Speaking at a European summit in Copenhagen, Denmark, Macron said that the French navy faced "inappropriate and extremely aggressive behavior" towards the French frigate and helicopters that had been deployed to board the taker, which justified the opening of a judicial investigation.

Stéphane Kellenberger, prosecutor of the western port city of Brest, said that two Chinese crew members, the captain and the chief mate, who had been detained since Tuesday, were released from police custody. The chief mate has been released without charge.

A preliminary investigation was opened into the crew's "refusal to cooperate" and "failure to justify the nationality of the vessel" after the Atlantic Maritime Prefect alerted justice authorities Monday, Kellenberger said. The inquiry showed the captain couldn't be directly considered responsible for the second offense, he added.

Kellenberger said that members of the French navy intervened and boarded the ship on Saturday off France's Atlantic coast in line with international law when there appeared to be a discrepancy between its apparent nationality and real nationality.

An investigation led by the French navy concluded that the ship, coming from Russia and heading to India with a "large oil shipment," was flying no flag, he said.

The captain was summoned for trial in Brest on Feb. 23. He faces up to one year in prison and a 150,000-euro ($176,000) fine.

French military spokesman Col. Guillaume Vernet said that the ship was ordered to stay in place in a safe area.

In comments earlier Thursday in Copenhagen, Macron praised the work of the French navy to "identify the presence of a shadow fleet."

"You kill the business model by detaining even for days or weeks these vessels and forcing them to organize themselves differently," he said.

Macron said "30 to 40%" of Russia's war effort is "financed through the revenues of the shadow fleet."

"It represents more than 30 billion euros. So it's extremely important to increase the pressure on this shadow fleet, because it will clearly reduce the capacity to finance this war effort for Russia," he said.

Macron said the ship was "exactly the same" one which was detained by Estonia earlier this year for the same flag issue.

In April, Estonian public broadcaster EE reported that the ship, then identified under the name "Kiwala," was stopped outside Tallinn Bay on way to the Russian port of Ust-Luga. At the time, Prime Minister Kristen Michal posted on social media that Estonia's navy had "detained a sanctioned vessel with no flag state" and authorities had boarded the ship -- without specifying.

The ship, now known as "Pushpa" or "Boracay," left the Russian oil terminal in Primorsk near St. Petersburg on Sept. 20, and sailed off the coast of Denmark. It has stayed off the coast of the French western port of Saint-Nazaire since Sunday, according to the Marine Traffic monitoring website.

The tanker, whose name has changed several times, was sailing under the flag of Benin and appears on a list of ships targeted by European Union sanctions against Russia.

Asked by journalists about it, Kremlin spokesperson Dmitry Peskov said that he had "no information" on the ship. He also said that many countries were carrying out "provocative actions" against Russia.

The shadow fleet is made up of used, aging tankers that were often bought by nontransparent entities with addresses from countries that haven't sanctioned Russia. Their role is to help Russia's oil exporters elude the price cap imposed by Ukraine's allies.

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Angela Charlton in Paris, Katie Marie Davies in Manchester, England, Jamey Keaten in Geneva, and Lorne Cook in Copenhagen, Denmark, contributed to the story.