A police investigation into a suspected jihadi cell in Arnhem has come unstuck after the suspects discovered a secret listening device hidden in the garden of one of their homes.

The receiver was spotted after the suspects noticed a displaced tile. They also found microphones, which had been attached to window frames, the Telegraaf says on Wednesday.

The men spread news and photos of the find on social media and gave the equipment to their lawyer who then passed it on to the police.

Six men were arrested after police raided nine houses in Arnhem, Doesburg, Rotterdam and Eindhoven at the end of last month.

The six are suspected of planning to join the terror group Jabhat al-Nusra, the Telegraaf says. Their passports were confiscated but they were not remanded in custody.