PARIS (AP) -- French police rescued the father of a wealthy cryptocurrency entrepreneur in a nighttime raid after he was taken hostage for ransom, the latest alleged criminal effort in France to extort people involved in the management of digital assets.

The man was kidnapped Thursday morning in Paris, the prosecutor's office said Sunday.

"The victim turned out to be the father of a man who made his fortune in cryptocurrencies, and the incident was accompanied by a ransom demand," its statement said, without giving their names or other specifics about their identities.

Police investigators located the hostage in a house in the Essonne region south of Paris, from which he was rescued on Saturday night, the prosecutor's office said.

It said he was treated for injuries but gave no details. French media reported that the alleged hostage-takers cut off one of the man's fingers.

Police detained 5 people -- four were in or close to the house where the man was held captive, while the fifth was at the wheel of a vehicle thought to have been used for the alleged abduction, the prosecutor's office said.

It said the police investigation is looking at an array of possible criminal charges, including kidnapping "with torture or a barbaric act."

In January, police said a co-founder of French crypto-wallet firm Ledger, David Balland, was also kidnapped with his wife from their home in the region of Cher of central France.

Police said they made 10 arrests and that the alleged kidnappers demanded a ransom in cryptocurrency from another of Ledger's co-founders.

A raid by France's elite National Gendarmerie Intervention Group unit that specializes in hostage situations freed Balland the next day, followed the day after that by the liberation, again by the GIGN, of his wife, found tied up in a vehicle, police said.