Ahmed Muhammad Jibril, a leader of the group and relative of the trio being held in a Bangkok prison, said the abducted man, identified as Sumanat Donut, would not be released until their demands are met.
"He is detained in Galkayo (the capital of Puntland) and won't be released unless our conditions are met," Jibril told AFP by phone from the town. "He is being treated well but will not be freed until our brothers are home safely."
Donut, who works for a Thai security firm, was abducted from a hotel in Puntland's port of Bossaso on October 21 and has been held incommunicado since, although pictures of him in captivity have been posted on Somali websites.
Jibril said Sumanat's abduction was no different from the detentions of the three Somalis, who were jailed by Thai authorities in April after being accused of piracy by the same security company.
"This abduction is not different from the one our brothers experienced while they were doing their duties," he said. "They were taken hostage by a Thai company, they are harassed in a Bangkok jail and that is why we have taken this man hostage."
Somalia has been without a functioning central authority since the 1991 ouster of dictator Muhammad Siad Barre and a transitional government set up in 2004 has been unable to assert control.
The government is increasingly challenged by the rise of a powerful Islamist movement that controls most of southern and central Somalia but has not yet extended its reach to Puntland, which operates as a semi-autonomous region.

Copyright AFP (Agence France-Presse), 2006