The demand was made through an Oslo solicitor, Tor Erling Staff. A spokeswoman for the Norwegian Embassy in London said: 'The solicitor says his client . . . has not stolen the painting, nor has it, but is able to return it against payment.'
She added: 'The solicitor, under no circumstances, will divulge his client's identity.'
Jens Kristien Thune, chairman of the board of the National Gallery in Oslo, said he could not comment before the gallery had decided whether or when to contact Mr Staff.
However, he added: 'That discussions involving the payment of considerable amounts of money to get stolen arts back is not very desirable.'
The painting was stolen in a 50-second robbery on 12 February - opening day of the Winter Olympics, when much of Norway's police force was in Lillehammer. Security cameras filmed the break-in and showed a man climbing into the gallery after smashing a window while an accomplice held the ladder.
Although a radical Norwegian anti-abortion group claimed knowledge of the theft, police remained sceptical. The pounds 700,000 ransom is said to represent 2 per cent of the painting's pounds 35m market value. On the illegal market, the more well-known and valuable a work, the harder it is to sell. Neither the police nor art experts believe that major, well-documented works are being stolen by a Mr Big collector - though a couple of Colombian drug barons have come to light as having a penchant for the Impressionists.
Stealing a famous picture and holding it to ransom has become known as 'art-napping'. One of the most important cases involving a ransom was a pounds 3m Brueghel taken from the Courtauld Institute in 1982: the thieves tried to sell it back to the gallery eight years later for a few thousand pounds. They failed, and are looking at more minimalist art - a prison cell.
Philip Saunders of Trace magazine, which liaises with the police and art world in tracking down stolen works of art, said that he could not see the Munch-ransom bid succeeding. 'No government would want to create a precedent of paying a ransom for a valuable work. Everybody would be in on the act - not just for money. Once one gives in, the rest will follow.'