The UK government has defended its seizure of a Russian “shadow fleet” oil tanker in the English Channel, after Russian President Vladimir Putin threatened to “respond in kind”.

The Smyrtos has been anchored off Weymouth after Royal Marines Commandos intercepted and boarded the vessel in a first-of-its-kind operation to disrupt the sanctioned tanker in June.

The vessel’s captain, Ajay Pant, has been charged with breaching Russian sanctions, accused of directly or indirectly supplying or delivering prohibited Russian oil.

Overseeing Russian navy drills in the Pacific Ocean, Putin scolded Western countries for “seizing our vessels”, branding such action “nothing other than piracy and banditry”.

Western nations allege Russia has been operating a “shadow fleet” of hundreds of vessels to evade international sanctions imposed on its oil exports.

These vessels stand accused of using complex ownership structures and various tactics to obscure the origin of their cargo, masking their link to Russia.

The UK Ministry of Defence says Russia has a fleet of more than 700 vessels, responsible for carrying 75% of the country’s sanctioned oil.

This oil is a “critical lifeline for the Kremlin” in “sustaining Russia’s illegal war” in Ukraine, the MoD says.

On Wednesday, Putin warned Western countries against seizing more of these tankers, saying: “If these plans are put into practice, we will have to respond in kind.

“And not necessarily in the waters where raids on our ships and vessels are planned, but wherever we deem it necessary and appropriate, anywhere.”

Viktor Liina, commander of Russia’s Pacific Fleet, accused Western countries such as Britain and France of operating their own “shadow fleets”.

“We have the capacity to inspect and detain vessels of unfriendly states and their shadow fleets, and interagency cooperation is in place, ready to begin addressing these challenges,” Liina said.

In response to Putin’s comments, the UK government said Britain’s armed forces and law-enforcement officers had boarded the Smyrtos “in full accordance with international law”.

“The UK is disrupting and deterring shadow fleet vessels and their harmful maritime activity which is fuelling Russia’s war with Ukraine,” a government spokesperson said.

The spokesperson said unlike Russia’s shadow fleet, “UK armed forces and commercial vessels operate firmly in line with international maritime law”.