Belgian authorities have boarded an oil tanker believed to be part of Russia’s shadow fleet, Belgian Defence Minister Theo Francken said on Sunday.

“Our armed forces, with the support of the French Defence, have boarded an oil tanker belonging to the Russian shadow fleet,” Francken wrote on X.

“The vessel is currently being escorted to the port of Zeebrugge, where it will be seized.”

The Belgian public prosecutor’s office said that the vessel “Ethera,” reportedly on its way back to Russia, appeared “to be sailing under the flag of Guinea, but there are indications that this is a false flag.”

During an on-board inspection “the indications of a false flag were confirmed, and ship documents were found that are suspected of being false.”

Sailing under a false flag “does not comply with several international regulations,” prosecutors said.

French President Emmanuel Macron said the joint operation was “a major blow to the shadow fleet.”

“Europeans are determined to cut off the sources of funding for Russia’s war of aggression in Ukraine by enforcing sanctions,” Macron wrote on X.

Belgian Prime Minister Bart De Wever congratulated the military on X for “the successful operation last night,” without elaborating.

He thanked France and added that Belgium would “uphold international maritime law and the security of its territorial waters.”

In a post on the X platform Ukrainian President Volodymyr Zelensky wrote “We welcome this strong action against Moscow’s floating purse and thank France for supporting the operation.”

He added that “Russia operates like a mafia organization, and the response must match that reality. If they reject the rules for the sake of war, the rules must foresee a clear and firm answer.”

The Russian embassy in Brussels stated that it had not been officially notified of the boarding of the oil tanker and the reasons for it. The embassy is currently clarifying whether there were any Russian citizens on board.

The shadow fleet is Russia’s response to the international oil-price cap imposed on the country’s fossil-fuel exports.

Moscow has been trying to conceal the origin of its oil using various methods like switching off or manipulating satellite transponders, or transferring oil between tankers on the high seas.

(L-R) Belgian Chief of Defence Frederik Vansina, Minister of Defence and Foreign Trade Theo Francken, Minister of Justice Annelies Verlinden and Minister of Climate and Mobility Jean-Luc Crucke attend a press conference of Belgian Defence regarding Operation 'Blue Intruder', at the naval base in Zeebrugge. Nicolas Maeterlinck/Belga/dpa

(L-R) Belgian Chief of Defence Frederik Vansina, Minister of Defence and Foreign Trade Theo Francken, Minister of Justice Annelies Verlinden and Minister of Climate and Mobility Jean-Luc Crucke attend a press conference of Belgian Defence regarding Operation ‘Blue Intruder’, at the naval base in Zeebrugge. Nicolas Maeterlinck/Belga/dpa