Belgian security services are fearful that ISIS operatives may have been looking to target a nuclear plant as it emerged two workers from a plant in Doel fled to Syria to join ISIS.
One of the men, reportedly known as Ilyass Boughalab, is believed to have been killed in Syria, while the second served a short prison sentence in Belgium for terror-related offences in 2014.
With an extensive understanding of nuclear facilities, the convict's short jail sentence has raised further questioned of the Belgian security services as well as fears he may have passed on important knowledge about the site's to the terrorist group.
The shocking revelations comes after the police claimed that the death of a security guard at a nuclear facility is being treated as a criminal act rather than a terror act.
Didier Prospero was shot several times in the bathroom of his home in the Charleroi region of Belgium.
The unidentified killers shot Prospero, who worked for G4S security at a Belgian nuclear research centre.
It had been feared the murder may be part of an ISIS plot to attack the facility and release radioactive waste into the atmosphere.
Or, the terrorists could have been planning to steal radioactive material to create a so-called dirty bomb.
Also, it is possible the terrorists wanted to sabotage a critical piece of machinery and cause the plant to meltdown, leading to a critical release of radioactive material.
Sebastien Berg, spokesman for the federal agency responsible for Belgium's nuclear industry said they were fearful of a bomb exploding inside a plant or terrorists conducting a 9/11-style attack using a hijacked aircraft.
Nuclear power plants are known to be targets for the terror network behind the Brussels bombings and the Paris attacks in November.
According to the New York Times, several employees working in the Belgian nuclear industry have had their security clearances revoked over potential ISIS plots.
Following last November's terror attack in Paris, Belgian police recovered surveillance footage of a senior nuclear official in the home of ISIS ringleader Mohamed Bakkali, who was arrested and is currently facing terrorism charges.
In a nation on high alert following this week's attacks, the report stokes fears about the possibility militants are seeking to get hold of nuclear material or planning to attack a nuclear site.
Such is the level of fear within the Belgian nuclear power industry, all non-essential staff at the Doel and Tihange power plants have been sent home.
A spokeswoman said: 'Only those who are really needed are staying, the other people were sent home.'
She said that for the foreseeable future Belgium's nuclear plants will continue operating with staffing levels similar to weekend service to ensure that no unauthorised personnel could gain access to the plants.
'Some 1,000 people work on sites like these. Their backgrounds are all checked thoroughly, but better safe than sorry.'
On Thursday, Derniere Heure newspaper had reported the suicide bombers who blew themselves up on Tuesday originally considered targeting a nuclear site, but a series of arrests of suspect militants forced them to speed up their plans and instead switch focus to the Belgian capital.
However, Charleroi prosecutors has reportedly played down reports of a connection between the murder and a planned terror attack, according to the Belga news agency.
Belga also said that the prosecutor had also denied media reports that the guard's access badge had gone missing...