French police are searching for a masked attacker suspected of stabbing an elderly woman to death in a retirement home for Catholic missionaries in southern France, according to authorities.

An unusually large police operation was launched to search for the suspected attacker on Friday, believed to be armed with a shotgun and a knife.

The identity of the attacker was unclear.

The press service for the gendarmes, or military police, also could not comment on the motive for the attack.

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Security at religious and other sites has been increased after a string of attacks in France in recent years.

A gendarme service spokesman said early on Friday that more than 100 members of the security forces were dispatched to the village of Montferrier-sur-Lez, near the city of Montpellier in southern France.

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Christophe Barret, a French prosecutor, said that a woman who works at the retirement home called the police on Thursday night to say she had been attacked.

When the officers arrived, they found the body of another woman, gagged and tied up outside the building with three stab wounds, the gendarme spokesman said.

The worker who alerted police did not suffer serious injuries but was badly shaken, and no one else at the residence was harmed, the prosecutor said in televised remarks carried on the website of Midi Libre newspaper.

Security forces searched the complex but did not find the assailant.

The spokesman said the 60 residents of the facility were out of danger, and the search is continuing in a larger perimeter with help from a helicopter and police dogs.

"One woman, a resident, was assassinated. The security forces have evacuated the residents, about 60, who are safe and sound," a police official told Reuters.

The official said the search in the building was over.

Retirement home

The residence, called Green Oaks, is operated by the African Missions Society, and takes in retired priests, nuns and others who have worked on missions in Africa.

Olivier Ribadeau Dumas, spokesman for the French Catholic bishops' conference, conveyed his condolences for the dead woman via Twitter: "Our prayers reach out also to the missionaries attacked in their retirement home in the Herault [region]. God give them all peace."

France has been under a state of emergency for a year since the attacks claimed by the Islamic State of Iraq and the Levant (ISIL) group in Paris killed 130 people.

At least 84 people were killed and 100 injured in the French city of Nice when a man deliberately drove a lorry into a crowd celebrating the country's main national holiday in July last year.

Another ISIL attack in July this year targeted a Catholic church in Normandy, where two attackers slit a priest's throat and held elderly parishioners hostage.

Source: News Agencies