FEARS are mounting Vladimir Putin's military have carried out a secret Arctic nuclear test after a huge spike in dangerous radiation levels were detected across Europe.

The worrying claims came as the US Air Force sent a special WC-135 Constant Phoenix - whose main mission is to detect and identify nuclear explosions from the air - to RAF Mildenhall.

3 The US Air Force sent a special WC-135 Constant Phoenix to RAF Mildenhall Credit: Digital

3 This map shows where high-level radiation particles have been detected since January

Along with monitoring nuke testing, the WC-135 is sometimes used to track radioactive activity as happened after the Chernobyl nuclear plant disaster in the then Soviet Union in 1986.

One of these aircraft was also deployed near North Korea in anticipation of Kim Jong-un's controversial rocket launches in recent years.

Although they cross European airspace from time-to-time, their deployment to the UK is still rare.

And there has been no official statement from the US military about the reasons why it has been sent here.

Sources suggest the aircraft has been tasked with investigating the spike in radiation levels detected in northern Europe since January.

And some respected websites claim there are growing fears within military circles that Russia has been testing its nuclear might ahead of a future conflict.

Many point to the radiation spike as "proof" the Russians have restarted nuclear weapons testing at Novaya Zemlya near the Arctic.

Others point to the lack of recorded seismic activity to cast doubt on the claims.

However, the deployment of the WC-135 to the UK seems to add weight to the test theory.

Tracking over the #UK 🇬🇧

🇺🇸 US Air Force

WC-135C Constant Phoenix

Nuclear explosion 'sniffer'

62-3582 COBRA55https://t.co/fvbSNtInVP pic.twitter.com/BB1WbDzAZK — CivMilAir ✈ (@CivMilAir) February 17, 2017

3 The USS Porter, armed with guided missiles, was buzzed by Russian jets off Romania Credit: Reuters

America's highest ranking military officer has compared current tensions with Russia to the height of the Cold War ahead of a face-to-face showdown with his Kremlin counterpart.

General Joe Dunford said an immediate meeting with Gen. Valeriy Gerasimov is “absolutely critical” as strains between the two superpowers reach breaking point.

Last Wednesday it was revealed Russian jets buzzed a US destroyer docked off the Romanian coast in a blatant show of force slammed by Navy officers as “unsafe and unprofessional”.

And a 200-crew Russian spy ship armed with surface-to-air missiles reached as close as 30 miles to the Connecticut coastline — and a key US submarine base.

At the weekend, the US Navy released a statement saying its testing of two Trident missiles was "not in response to any world events" after scores of people filmed a mysterious light trailing through the night sky.

Yesterday, we revealed how radioactive particles had been detected in seven different European countries and scientists can't explain where they have come from.

Traces of Iodine-131 were found in Norway, Finland, Poland, Czech Republic, Germany, France and Spain in January but the public were not immediately alerted.

These radioactive particles are produced by atomic bomb explosions or nuclear disasters such as Chernobyl or Fukushima.

Related Stories MAP SCRAPPER Stop iPhone apps spying on your EXACT location now with new 'scramble' feature STOCK SHOCK Will there be more PS5 pre-orders? Sony's latest console sells out in minutes Pictured EARLY BIRDS Apple fans queue for new Apple gadgets in first 'socially distanced' launch day NEXT TOP MODEL PS5 sold out almost EVERYWHERE – here's where you might still get one today X MARKS THE SPOT Couldn't get a PS5? Xbox Series X pre-orders start next week in UK and US GAMER GOLD Can you play PS4 games on PS5? PlayStation backwards compatibility revealed Review ALL A-BOARD! Tony Hawk Pro Skater 2020 review – a ‘90s classic now better than ever in 4K APOCALYPSE WOW Stunning new Jupiter photo shows 9,800-mile MEGA storm bigger than Earth CAR KIPPER COPPED Reckless Tesla driver 'caught SLEEPING at 93mph in autopilot mode' TAP TIPS Apple's update just gave your iPhone a new 'button' – and it'll make life easier

They appear to be emanating from Eastern Europe but experts have not been able to say exactly what produced them.

Astrid Liland, head of emergency preparedness at the Norwegian Radiation Protection Authority, told the Barents Observer that the health risk was very low - which was why she did not raise the alarm after detecting Iodine-131 during the second week of January.

“We do measure small amounts of radioactivity in the air from time to time because we have very sensitive measuring equipment," she said.

"The measurements at Svanhovd in January were very, very low. So were the measurements made in neighbouring countries, like Finland. The levels raise no concern for humans or the environment. Therefore, we believe this had no news value."

However, she was unable to say where the particles have come from.

They may have been released by accident by a nuclear reactor or a medical facility where they are being used to treat hyperthyroidism and thyroid cancer.

The particles could also been produced by Russian nuclear submarines.

What does the WC-135 Constant Phoenix do? The WC-135, known as the “sniffer” or “weather bird” by its crews, can carry up to 33 personnel. However, crew compliments are kept to a minimum during mission flights in order to lessen levels of radioactive exposure. Effluent gasses are gathered by two scoops on the sides of the fuselage, which in turn trap fallout particles on filters. The mission crews have the ability to analyse the fallout residue in real-time, helping to confirm the presence of nuclear fallout and possibly determine the characteristics of the warhead involved. The WC-135 was introduced in December 1965, replacing Boeing WB-50 aircraft in the weather-reconnaissance and air-sampling mission. While most aircraft were placed into storage after the Cold War, three were retained for further use.