Belgium's special forces, assisted by France, boarded and seized an oil tanker from the so-called Russian shadow fleet used to circumvent Western sanctions over the war in Ukraine, in an overnight operation announced on Sunday.
The Belgian government said the "vessel from Russia's shadow fleet" was intercepted in the North Sea, with aerial support from French military helicopters.
Defense Minister Theo Francken said the tanker was escorted to the port of Zeebrugge after being intercepted in Belgium's exclusive economic zone.
Prosecutors identified the ship, which was said to be on its way back to Russia, as the "Ethera."
A spokesperson for the Belgian federal prosecutor's office said the ship captain, a Russian national, was being questioned by investigators.
The tanker flew the flag of Guinea, but an onboard inspection confirmed suspicions that it was sailing under a false flag, the office said.
"Ship documents were found that are suspected of being false," prosecutors said in a statement, adding that authorities have opened a criminal investigation.
"If a ship sails under a false flag, this means that it does not comply with several international regulations," the statement added.
French President Emmanuel Macron confirmed on X that his country's naval forces assisted in the operation, calling it a "major blow" to Russia's so-called "shadow fleet."
Russia has used a flotilla of ageing tankers of opaque ownership to get around restrictions on its lucrative crude exports imposed over its 2022 all-out invasion of Ukraine.
The Belgian Defense Ministry said the seized tanker was on the European Union's sanctions list. The EU has blacklisted hundreds of vessels in a bid to sap Moscow's war chest.
"Sanctions only matter if they are enforced. Today, we enforced them," Foreign Minister Maxime Prevot, who is also Belgium's deputy prime minister, said on X.
The operation was carried out alongside Belgium's G-7, Nordic and Baltic partners and in coordination with France, he added.
France provided air support with two NH90 helicopters, the Defense Ministry said.
Footage of the operation posted online by Macron showed Belgian forces rappelling down from the aircraft to board the ship.
"I congratulate our armed forces on their professional and decisive conduct during tonight's successful operation, and thank our French partners for providing essential support," Belgian Prime Minister Bart De Wever wrote on social media.
Russia's embassy in Belgium said it had not been officially notified of the tanker's detention, nor informed about the nationality of its crew.
"The embassy is currently taking the necessary steps to determine whether there are Russian citizens on board and to ensure their legal rights if confirmed," it said in a Telegram post.
Sanctions aimed at limiting Moscow's revenues used to pursue its war have shut out many tankers carrying Russian oil from Western insurance and shipping systems.
Some experts and political leaders also suspect "shadow fleet" vessels of carrying out sabotage, as part of a "hybrid war" by Russia against Western countries.
Ukrainian President Volodymyr Zelenskyy welcomed Belgium's "strong action against Moscow's floating purse" and thanked France for supporting the operation.
"This particular vessel has long been under U.S., EU, and U.K. sanctions, but nonetheless continued to illegally transport Russian oil using a false flag and forged documents," he wrote on X.
Ukrainian Foreign Minister Andriy Sybiha added that "such resolute and justified action" was required to deprive Russia of resources to continue its war against Ukraine.
"We urge all partners to follow this example, counter Russia's shadow fleet resolutely through sanctions and concrete action, and advance peace through strength," he said.
In February, it was revealed that two employees of a Russian private security company were aboard another suspected Russian "shadow fleet" tanker seized by France in September.
The two men were employed by Moran Security Group, a Russian private security company, and were tasked with monitoring the crew and gathering intelligence, a source with knowledge of the matter told Agence France-Presse (AFP).
French forces boarded another suspected Russian tanker, the Grinch, in January.
