British military units stopped a Russian shadow fleet oil tanker sailing through the English Channel early on Sunday, according to Sir Keir Starmer.

Royal Marine Commandos joined National Crime Agency officers for a six-hour boarding action on the ship, with backing from RAF units.

The tanker named Smyrtos remains under watch off England's south coast while inquiries proceed, the Ministry of Defence confirmed.

Sir Keir Starmer stated that the action strikes another hit against Russia and shows those supporting Putin's Ukraine campaign they cannot evade detection.

MarineTraffic data shows Smyrtos flies the Cameroon flag and sits at anchor in the Channel.

Russia relies on a shadow fleet of tankers to bypass sanctions on its oil shipments.

The fleet of more than 700 ships moves 75 percent of Russia's sanctioned oil and serves as a key revenue source for the Kremlin, the MoD noted.

In March the prime minister declared that UK forces could now board sanctioned ships in British waters.

The MoD added that Britain has placed sanctions on over 500 vessels.

These measures bar the ships from UK ports and stop British companies or people from offering financial, insurance or brokerage help to vessels carrying Russian oil.

The boarding follows a week of departures linked to delays in the government's defence investment plan, due before next month's Nato summit.

John Healey stepped down as defence secretary on Thursday, saying the proposed spending level does not meet needs for UK security.

Labour MP Pamela Nash also left her role as Healey's parliamentary aide at the MoD over funding delays for the plan.

Sunday's action drew support from Maritime Air Group planes, an RAF P-8 aircraft, HMS Sutherland and HMS Ledbury.

Attorney General Richard Hermer noted that the government would apply international law fully against Russia's shadow fleet.

Officials aim to cut Russia's oil income to limit funds for its Ukraine operations.

The Sunday morning boarding involved close cooperation with France, the MoD said, following earlier UK assistance to allies.

French President Emmanuel Macron reported on 1 June that his forces had stopped a suspected shadow fleet tanker that day with UK help.