Some 100 police officers are searching for a gunman suspected of stabbing an elderly woman to death in a retirement home for Catholic missionaries in southern France.

A spokesman for the gendarmerie, or military police, said on Friday the searches are continuing in a larger area, with help from police dogs, around the village of Montferrier-sur-Lez, near the city of Montpellier.

He said all possible motives for the killing are being explored and he couldn't rule out a terrorist act at this point. He was not authorized to be publicly named.

The identity of the masked assailant, believed to be armed with a shotgun and a knife, remains unclear.

The body of the woman was found late Thursday, gagged and tied up outside the building with three stab wounds.