Could Isil obtain a nuclear device? In 90 secondsPlay!01:32
Ibrahim and Khalid el-Bakraoui, the brothers behind the suicide strikes on Brussels airport and Metro, are believed to have been involve the plot to scatter radioactive material over a populated area.
A senior Belgian nuclear industry official was secretly filmed by jihadists late last year, according to the country’s nuclear authority, and the brothers were linked to the surveillance.
First flight leaves re-opened Brussels airportPlay!00:47
There are also concerns over Belgium’s ageing nuclear plants that have been subject to repeated safety warnings, including defects in pressure vessels and fires.
Last week Germany asked that the 40-year-old Tihange 2 and Doel 3 reactors be turned off "until the resolution of outstanding security issues".
The reactor pressure vessels at both sites have shown signs of metal degradation, raising fears about their safety. They were temporarily closed but resumed service last December.
Belgium's official nuclear safety agency (AFCN) rejected the German request, saying the two plants "respond to the strictest possible safety requirements."
The key figure in the suspected dirty bomb plot is Mohammed Bakkali, 28, from Brussels, who was arrested in November on suspicion of helping to plan the Paris massacre. Police raided his wife’s flat and found a ten-hour video taken by a camera hidden opposite the home of an executive at the Centre for the Study of Nuclear Energy in Mol, northern Belgium. The executive had access to radioactive isotopes at the country’s national nuclear research centre.