The US is planning to seize a sanctioned Venezuelan oil tanker off the coast of Ireland.
The Bella 1evaded capture in the Caribbean Sealast month, but has been spotted in the Atlantic, around 500 miles from Ireland's west coast.
American military aircraft flying from RAF Mildenhall in Suffolk have been monitoring the vessel in recent days, according to flight tracking data.
RAF Typhoon fighter jets, accompanied by KC2 aerial refuelling tankers, have also been tracked flying towards the last known location of the tanker.
The US coast guard had tried to intercept the Bella 1 as it sailed toward Venezuela to pick up oil beforethe arrest of president Nicolas Maduro.
The tanker's crew has since painted a Russian flag on its side in an apparent bid to claim Moscow's protection, while the vessel was re-registered in Russia as the Marinera.
Russia, if it claims ownership of the vessel, could issue a sternly worded statement, but there is no precedent for further escalation in other cases of detained shadow fleet vessels.
American military transport planes that carried helicopters known to be used in clandestine special forces operations landed at RAF Fairford in recent days.
Two officials, cited in a report by CBS News, said US forces would rather seize the vessel than sink it.
Any operation could replicate one carried out last month when US Marines, special forces units and the coast guardcaptured the Skipper, an oil tanker, after it left a port in Venezuela, they added.
Credit: X/@AGPamBondi
The mission could come as soon as this week, CBS reported, but could ultimately be shelved.
Donald Trump appears to be maintaining his pressure campaign on Venezuela's economy despite capturing its long-time dictator from his home in Caracas last week.
As the world came to terms with the US president's special forces operation, as many as 10 C-17A Globe Master transporter planes landed in Britain.
Some of the aircraft flew from army airfields Campbell and Hunter, which are best known as the homes of the 160th Special Operations Aviation Regiment.
Upon arrival in Fairford, American personnel unloaded Chinook and Black Hawk helicopters, both used by the regiment for clandestine operations. These aircraft were used in the raid on Maduro's Caracas home.
A spokesman for the US air force refused to confirm the details of the operation.
They said: "US Air Forces Europe – Air Forces Africa routinely hosts transient US military aircraft (and personnel) in accordance with access, basing, and overflight agreements with allies and partners. Taking into account operational security for US assets and personnel, further details are not releasable at this time."
But analysts speculated that the movement of equipment could be linked to a potential mission to seize the Marinera.
Matthew Savill, director of military sciences at the Royal United Services Institute (RUSI), said the build-up could hint towards several potential missions.
The defence expert said it could range from building up forces for a potential operation in the Middle East or Africa, to preparing a mission to board the Bella 1.
He added: "But it could be a cunning misdirection. When they launched Midnight Hammer (to strike Iranian nuclear facilities) they had one thing tracking with transponders on.
"It's not implausible that while we're all watching that, there's something flying around over there that we're not seeing."
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