French police have clashed with striking prison guards at Europe’s largest jail on the fourth day of walkouts across the country over security concerns.

Officers fired teargas as scuffles broke out at the Fleury-Mérogis prison, south of Paris, where guards are protesting after a series of attacks on staff.

The French president, Emmanuel Macron, has promised to draw up a national prisons plan to address concerns by the end of February.



The attacks that sparked the guards’ protest have highlighted security problems and radicalisation inside often overcrowded French prisons.



In the latest outbreak of violence, two guards were attacked by four inmates at the Borgo jail in Corsica. The guards were taken to hospital in a serious condition and the four inmates were arrested after gendarmes moved in to secure the prison, a penitentiary official said.

Outside the entrance to Fleury-Mérogis jail, which has more than 4,300 inmates, about 150 striking guards built a barricade of burning tyres and wooden pallets to prevent their colleagues from getting to work

A unit of CRS riot police broke through the picket line, firing teargas to disperse the demonstrators and allowing other staff to enter the prison while striking guards were held behind a barrier.



“The CRS charged and fired teargas at us but we tried to resist,” a 28-year-old guard who gave his name as Sacha told AFP.



Police stand near striking guards and burning wooden palettes at the Vendin-le-Vieil jail in northern France on Tuesday. Photograph: Francois Lo Presti/AFP/Getty Images

On Thursday, about 120 prisoners refused to return to their cells after their midday walk in the yard. They were brought back in with the help of specially trained intervention teams, France’s prison administration service said.



Six prisoners who are thought to have led the protest were sent to the punishment block, a prison officers’ union source said.

Despite talks to resolve the protests and pledges by Macron to outline plans for an overhaul of French prisons, the unions decided to continue the industrial action.

The strike began on 11 January after a German convict, a former top al-Qaida militant, attacked three guards with scissors and a razor blade at a high-security prison in northern France.



On Thursday, guards at more than 123 facilities were “mobilised”, the UFAP-UNSA and the CGT unions said.



Figures provided by the prisons’ administration said 87 of the country’s 188 detention facilities had been affected by the strike action.

In a statement this week, Force Ouvrière, one of the unions involved in the strike, said two-thirds of France’s prisons had been hit by industrial action.



Prison staff were protesting against “the absence of consideration for personnel and an absence of equipment, notably security material in penitentiary establishments”.



Union officials have been holding talks with the justice ministry over longstanding complaints of low pay, insufficient staffing and overcrowding at prisons.



Guards warn that their safety is at risk after several attacks by prisoners linked to Islamic extremism or under surveillance because of the risk of radicalisation.