French prison guards blocked access to 18 prisons on Wednesday after an inmate in the north of the country wounded two guards in what the justice minister said was a terrorist attack.
Michaël Chiolo was apparently given a knife when his female partner visited a high-security jail in Normandy.
They barricaded themselves into a family-visiting area before police eventually moved in.
Unions called for action at all prisons over safety and staffing.
france has for years had to grapple with the spread of jihadism in its jail system.
The head of Condé-sur-Sarthe jail near Alençon, where the attack took place, was seen unsuccessfully appealing to protesting guards to be allowed in. Tyres were set on fire and when police arrived they were jeered as the guards stopped them getting through.
A hundred guards refused to let anyone into another high-security jail at Fleury-Mérogis, news channel BFMTV reported.
One guard, Cédric, told the Ouest france website that he had treated the two guards stabbed in the attack. “It was carnage, the ferocity of it. I’m thinking of my colleagues and I worry tomorrow that might be us.”
What happened in the jail?
At 09:45 on Tuesday, Michaël Chiolo, a 27-year-old inmate thought to have been radicalised in jail several years ago, was visited by his 34-year-old female partner in a special “family life” visiting unit. It was thought she had smuggled in a ceramic knife, Justice Minister Nicole Belloubet said.