CONDE-SUR-SARTHE, France (Reuters) - The partner of a French prison inmate was killed by police on Tuesday after they stabbed two guards in an attack the government called a terrorist incident.

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After the stabbing, the couple barricaded themselves in a room used for family visits in the top security jail in Conde-sur-Sarthe, northern France for ten hours before police stormed the room, anti-terrorist prosecutor Remy Heitz said.

A source from the prison guards union said the woman, who was not named, was shot.

She was visiting her companion, named as Michael Chiolo and serving a 30-year sentence for armed robbery, kidnapping and murder, when the attack took place.

Heitz said Chiolo, who was slightly wounded by police, shouted Allahu Akbar (God is Greatest) during the stabbing.

“(He) said he wanted to avenge Cherif Chekatt,” Heitz told reporters. “He said he was wearing an explosive belt and threatened to use it.” The belt turned out to be fake.

Chekatt killed five in a terrorism attack in Strasbourg in December.

French prisons have been fertile breeding grounds for the spreading of radical Islamist ideas. Most of those responsible for a series of attacks that have hit the country in recent years had spent time in jail before striking, and radicalized inmates have repeatedly attacked guards.

Justice Minister Nicole Belloubet earlier said she understood the prisoner was on a security agencies watch list of potential threats because of his suspected Islamist sympathies.

“There is no doubt about the terrorist nature of this attack,” Belloubet told reporters.

She said an investigation was under way into how Chiolo’s companion was able to smuggle a ceramic kitchen knife into the prison.

While in the prison, Chiolo was convicted of publicly condoning terrorism.