French police are questioning several people after seizing 100kg (220lb) of Semtex explosive hidden in a lorry in the northern town of Hazebrouck.
The operation on Saturday was part of an investigation into organised crime. The plastic explosive was allegedly bound for Paris.
Hazebrouck lies 30km (20 miles) from the Channel port of Calais and is also near the Belgian border.
Semtex – a Czech-made explosive – has been used by various terrorist groups.
The French prosecutor’s office said it believed the Semtex seized on Saturday was to be divided up and sold to criminal gangs, rather than to terrorists, Reuters reported.
No details about the suspects were released.
Observers say Semtex can be hard to detect and as little as 250g can bring down an airliner.