The seven, an expatriate employee of GDF Suez, his wife, four children and an uncle, were found in a house in the Nigerian town of Dikwa, the French BFMTV television channel reported Thursday morning.
Junior French government minister Kader Arif confirmed the news shortly afterwards but then withdrew his statement, saying that his only sources were the news media.
A Cameroonian military source had already told news agencies that the hostages were freed.
They were reported to have been left their by their captors, who may have had second thoughts about holding children hostage, according to some analysts, and to have been in the hands of the Nigerian authorities.
The French foreign ministry declared Arif's announcement "astonishing" by the news and said it could not confirm the report at 10.15 am Thursday and the presidency could not confirm, either.
Later reports from Cameroon said that the family was being transported from Nigeria to Cameroon but a Cameroonian minister denounced the whole story as "a crazy rumour".