France, May 2 -- French anti-terror prosecutors have handed over the investigation into a spate of violent attacks on prisons, saying that the violence is linked to drug gangs rather than terrorism.

At least 10 prisons were targeted over five nights in April. Cars were torched in prison car parks, mortars were fired at detention centres and prison staff were threatened at their homes. In one incident, automatic gunfire hit a housing estate where prison guards live.

On Friday, the national anti-terror prosecutor's office (PNAT) said it no longer believed the attacks were part of a terrorist plot.

"It does not appear that these coordinated actions stem from a terrorist enterprise," said PNAT. "No radical violent ideology, no foreign inte...