Authorities in several European countries reopened unsolved murder and disappearance cases going back 30 years on Thursday after a French forest warden confessed to raping and killing six girls in Belgium and France.

A Belgian prosecutor said Michel Fourniret, 62, nicknamed the "Ogre of the Ardennes" by the French media, may well have killed more people than he has admitted.

Fourniret has been in custody in Belgium since last year over a separate abduction but confessed only this week to six killings after his estranged wife denounced him to police. She accused him of nine murders.

Dutch police said on Thursday they would contact Belgian authorities to seek new leads on several disappearances.

"We have had some cases of missing young people in the past and we will see what we can do with the information when we have contacted our Belgian colleagues," said a police spokesman in Limburg-Zuid, close to the Belgian border.

French authorities said they planned to re-open files dating back to the 1970s on disappearances and unsolved killings of young girls near the Franco-Belgian border and across France.

French investigators suspect Fourniret of killing at least 10 people - eight girls and two adults - including the partner of Jean-Pierre Hellegouarch, a suspected member of the French extreme-left urban guerilla group Action Directe.

Fourniret met Hellegouarch, thought to be the group's treasurer, in prison and said he used the movement's funds to buy the Sautou chateau, with about 13 hectares of grounds, near Sedan, a claim the Reims public prosecutor's office described as "extravagant".

A French judicial official said soldiers were ready to dig for the corpses of Fourniret's victims and some would go to the chateau. Fourniret had admitted burying at least two bodies near the property, the official said.