This undated handout provided by the Norwegian police shows wife of Norwegian multi-millionaire Tom Hagen, Anne-Elisabeth Falkevik. Image Credit: AFP

Oslo: The wife of a Norwegian multi-millionaire missing for 10 weeks has probably been kidnapped and a ransom has been demanded for her release, police said on Wednesday.

Married to a real estate and energy magnate, 68-year-old Anne-Elisabeth Falkevik Hagen disappeared on October 31, police said.

"A ransom demand and serious threats have been issued," inspector Tommy Broske told reporters.

"Our main theory is that the victim was kidnapped by unidentified perpetrators at her home" in Lorenskog, about 20 kilometres from Oslo, he said, adding that police have from the beginning examined several possible theories about her disappearance.

Police have received no sign of life from the woman, "but we haven't received any indication that she isn't alive either," Broske said.

The cautious nature of the remarks could be an indication that police have not received proof that Hagen was indeed being held by the people demanding the ransom.

Police said they had no suspects at this stage.

According to daily Verdens Gang, the ransom demand was for nine million euros ($10.3 million;Dh37 million) in the cryptocurrency Monero.

Unusual trouble

Investigators refused to confirm that amount but said they advised the family not to pay the purported kidnappers.

Such events are extremely rare in the wealthy Scandinavian country, which enjoys a generally low crime rate.

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Police have been investigating the case discreetly for several weeks but decided to make it public in the hope that someone would come forward with information, Broske said.

Broske said investigators had had "very limited" contacts with the self-described kidnappers online, but refused to disclose the date of the most recent contact.

The missing woman's husband, Tom Hagen, also 68, is Norway's 172nd richest man, according to the magazine Kapital, with an estimated fortune of 1.7 billion kroner (174 million euros, $200 million).

The real estate investor owns 70 per cent of electricity company Elkraft, which he co-founded in 1992, Norwegian media reported.