The al-Qaeda group says it seized Frenchman Pierre Camatte in Mali
A branch of the al-Qaeda network is demanding the release of four of its members in exchange for a Frenchman it says it kidnapped in Mali last month.
The group issued its demand on an Islamist website, according to two US monitoring groups.
Pierre Camatte was taken from his hotel by gunmen in Menaka in Mali on 25 November.
Four days later, three Spanish aid workers were snatched from an aid convoy in neighbouring Mauritania.
There has been no sighting of the four Europeans since the kidnappings.
The statement, issued on Sunday by the north African branch of al-Qaeda, sets an ultimatum of 20 days for the exchange, after which, it says, the French and Malian governments "will be fully responsible for the French hostage's life".
Warning to visitors
A Malian official has said the demand amounts to "blackmail".
A source close to the negotiators told the AFP news agency that the group was also demanding a ransom to free Mr Camatte.
The source said it was "a lot of money", without specifying the amount.
The UK recently warned its nationals not to visit northern Mali because of the threat of attack by the north African branch of al-Qaeda.
The militants were believed to be behind the murder of British hostage Edwin Dyer in June.
Also in June, an American teacher was killed in Mauritania, with the same group later claiming it had killed him for spreading Christianity in the Islamic state.