Doel nuclear plant, Belgium
A security guard at the Doel nuclear plant in northern Belgium was murdered on Thursday 24 March.Reuters

A Belgian nuclear plant worker has been shot dead, and his security pass stolen, in a murder which has raised fears that Islamic State (Isis) linked terrorists are trying to build a radioactive 'dirty bomb' – or even a primitive atomic bomb.

The man, who worked as a guard at the Doel nuclear plant, was out walking with his dog on Thursday evening in the city of Charleroi when he was killed, La Derniere Heure newspaper reported on Saturday.

The plant deactivated the dead security guard's pass after security services discovered what had happened. While the motive for his murder was unclear, there are concerns that terrorists have been trying to get hold of radioactive material.

His death comes after an unidentified senior nuclear official in Belgium, who had access to secure areas of a nuclear research facility in the town of Mol, was allegedly put under surveillance by an Islamist cell.

Police found video footage of him entering and leaving his home in the Flanders region when they arrested a 26-year-old man on charges of terrorist activity and murder following the attacks on Paris in November.

Speaking this week, an official at Belgium's Federal Agency for Nuclear Control told The Times: "When you start filming someone in the way they did, the logical conclusion is that they wanted to abduct that person and to obtain radioactive material."

What is a dirty bomb?

The device uses conventional explosives to spread radioactive material over a wide area, which could be contaminated for years as a result. However experts have warned that more people could be killed by the resulting panic than the radioactivity itself.

According to the US Nuclear Regulatory Commission, the health effects of exposure to the radiation from a dirty bomb would be "minimal".

Security passes of 11 staff at the Tihange nuclear power station were also recently withdrawn as a result of vetting by a committee of intelligence and security experts.

According to unconfirmed reports, two of the suicide bombers involved in the murders of at least 31 people in Brussels on Tuesday – brothers Khalid and Ibrahim El Bakraoui – were planning to attack a nuclear site in the country. The Doel plant is said to have increased its security measures as a result.

However on Thursday, Yukiya Amano told the AFP news agency that dirty bombs could drive "any big city in the world into panic", warning that the "psychological, economic and political implications would be enormous".

And he added it was "not impossible" that extremists might be able to make a "primitive" nuclear bomb capable of a fission explosion.

"It is an old technology and nowadays terrorists have the means, the knowledge and the information," he said.

Brussels explosions: Security analyst claims attacks prove existence of 'susbtantial network' of terrorists in EuropeIBTimes UK