A French prosecutor says a suspect with no apparent link to Islamic terrorism has been identified following the stabbing death of an elderly woman in a retirement home for Catholic missionaries in southern France.

Montpellier prosecutor Christophe Barret said the suspect is believed to be someone "in the entourage of this retirement home".

He said investigators have discovered an air gun and other elements that he wouldn't detail in a car near the residence that helped identify the suspect.

Some 100 police officers are still searching for the suspect following the attack on the woman on Thursday evening.