French police are treating the stabbing of two prison guards by a suspected Islamist inmate as a terrorist attack.

Elite officers used stun grenades to capture the prisoner after he stabbed security staff with a ceramic knife before barricading himself in a room used for family visits.

The man reportedly shouted “Allahu Akbar” [God is greatest] as he launched the attack while his wife was visiting the Normandy prison on Tuesday, prison officials were quoted as saying.

Nicolas Castaner, the French interior minister, confirmed the prisoner and his wife had been detained by officers.

Nicole Belloubet, the justice minister, said she understood the prisoner was on a security agencies' watch list of potential threats because of his suspected Islamist sympathies.

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She said: “There is no doubt about the terrorist nature of this attack.”

The minister added that one of the guards had been seriously injured.

French police take position outside the prison where an inmate stabbed two guards with a knife in Conde-sur-Sarthe, France, on 5 March 2019. (Reuters/Benoit Tessier)

The inmate at the centre of the attack was serving a 30-year sentence for murder, armed robbery, kidnapping and publicly condoning terrorism at the prison in Conde-sur-Sarthe, roughly half way between Caen and Le Mans.

He was jailed in 2015 for the offences, which included the murder of an 89-year-old man who had survived Nazi concentration camps.

French media reported the inmate as being known as a radicalised Islamist.

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An investigation has been launched to find out how the prisoner got hold of a knife and whether his wife was involved.