A previously unknown terrorist group Tuesday demanded a $790,000 ransom for the release of Paul Vanden Boeynants, the former Belgian prime minister it claims to have kidnapped.

In a one-page typewritten letter, the Revolutionary Socialist Brigade demanded that two-thirds of the ransom come from Vanden Boeynants' political and business partners and be given to the poor, according to deputy Brussels prosecutor Andre Vandoren.The rest of the ransom would be for the group's "participation in the effort to mobilize the people."

The letter, delivered to Brussels dailies Le Soir and Het Laatste Nieuws, called Vanden Boeynants "a corrupt person who has stolen large public funds for his own profit" and called for a "people's tribunal" to try him.

Vanden Boeynants, 69, a businessman and Christian Democrat politician who disappeared Saturday, is under investigation for taking bribes when he was defense minister for seven years in the 1970s.