The disturbing discovery was made after officers from the Office for the Protection of Constitutional Officials and Diplomatic Missions came across the envelope while sorting correspondence on Wednesday.

The envelope was sent anonymously, and the bullet was found following an X-ray examination.

“We can confirm that the envelope with the bullet addressed to the Prime Minister of Slovakia has been delivered today to the Chancellery of the Government of the Slovak Republic,” the prime minister’s office told the Slovak news website Aktuality.

Police have now launched an investigation, the government’s press department told the news website POLITICO.

The incident has renewed concerns about Fico’s safety, who survived an assassination attempt in May.

Fico was shot with four bullets at close range when he greeted supporters at a government meeting in the central Slovak town of Handlová.

The attack left him in a serious condition, needing hours of surgery.

The perpetrator, identified as 71-year-old Juraj Cintula, said that the attack was carried out on political grounds, adding that he disagreed with Fico’s policies.

He is currently in custody and faces 25 years to life in prison.