TWO men stumbled on “deadly radioactive poison” – historically used by Russia to assassinate its critics – during an Easter egg hunt.

Instead of chocolates, a bottle labelled “Polonium 210,” a rare isotope, was unearthed in the back garden of a house in the German city of Stuttgart.

NINTCHDBPICT001071671930File photo of a fire truck in GermanyCredit: Alamy NINTCHDBPICT001071671881A stock pic of a police officer in Bavaria, GermanyCredit: Alamy

What started as a report to ended in 138 emergency personnel and 41 vehicles deployed to the scene in Vaihingen an der Enz.

A radiation protection unit was also dispatched after the discovery of the white plastic bottle with a red lid.

“The label isn’t just scribbled on by hand; it’s clearly and officially marked,” a spokesperson for the fire department said.

While tests are yet to be conducted, the vial is considered to be “genuine.”

The liquid – estimated to weigh 200 grams – is relatively heavy, making it consistent with the fact that polonium-210 is a relatively dense substance.

Often described as the perfect poison, it was behind the killing of critic and .

After he defected to the UK in 2000, he became a staunch critic of and started working for MI6 as a consultant.

He was poisoned with radioactive polonium-210 in London in 2006 during a meeting with former KGB agents Andrei Lugovoy and Dmitri Kovtun at London’s Millennium Hotel, and died in agony three weeks later.

On his deathbed, of ordering his murder.

The death of Palestinian political leader Yasser Arafat in 2004 is also widely suspected to be a polonium-210 assassination.

Swiss scientists found levels 18 times higher than normal in his remains in 2013.

Once ingested, the isotope is hard to detect as all the radiation remains in the body.

A lethal dose could be as little as a few milligrams, administered either as a powder or dissolved in liquid.

It is one of several radioactive poisons that could be unleashed as a lethal weapon whilst causing the murderer no harm.

If stored in a glass bottle, similar to the one in Stuttgart, the radiation is kept inside.

The German Ministry for the Environment will now test what is hidden inside.

Whether the vial actually contains polonium still needs to be definitively determined.

Former Russian Agent Poisoned In LondonAlexander Litvinenko is pictured at the Intensive Care Unit of University College Hospital on November 20, 2006 in LondonCredit: Getty