The six-hour operation in the early hours was supported by aircraft, including Chinook helicopters, and navy vessels such as the frigate HMS Sutherland.

"In the first UK-led operation of its kind, the vessel SMYRTOS was boarded by Royal Marine Commandos and specially trained law enforcement officers from the National Crime Agency, despite Russia's best efforts to evade sanctions and continue fuelling its barbaric war with Ukraine," the ministry statement said.

The vessel will now be moved to an anchorage off the south coast of England and monitored, it added.

"Russia relies on its shadow fleet to fund their conflict in Ukraine and our interdiction delivers a blow to Putin's illegal war," said defence minister Dan Jarvis.

He said the operation was carried out in "close coordination with the French".

Disrupting the shadow fleet was "directly bearing down on the resources sustaining Russia's aggression in Ukraine and reducing its capacity to threaten security across Europe and beyond", he added.

The UK has sanctioned hundreds of vessels suspected of being part of the shadow fleet used by Russia to bypass Western embargoes since the invasion of Ukraine in 2022.

The ships -- usually ageing tankers with dubious ownership -- are banned from accessing UK ports and services.

Prime Minister Keir Starmer said the operation delivered "yet another blow to Russia and reminds those fuelling Putin's war in Ukraine that they cannot hide".

In March, the government announced that British forces would be able to board and seize shadow fleet vessels passing through its waters.

The announcement followed the easing of restrictions by Washington on Russian oil to soften prices sent soaring by the US-Israel war against Iran.

France, Belgium, Finland and other European countries have also recently seized sanction-busting vessels believed to belong to the so-called shadow fleet.