PARIS (Reuters) - The father of a family of seven French tourists kidnapped by a Nigerian Islamist group read out a threat by them in an audio tape to increase kidnappings and suicide bombings in Cameroon if authorities there detain more of the group's followers.

Tanguy Moulin-Fournier, in a tape obtained by local journalists in Nigeria on Monday and whose authenticity was being checked by the French Foreign Office, appealed to the government of Cameroon, where his family was kidnapped last month, to free prisoners of Islamist sect Boko Haram as a condition of the family's release.

"They don't want to enter in conflict with Cameroon. However, if you arrest their men again in Cameroon, they will multiply kidnapping and suicide bombing operations more in Cameroon than in Nigeria," Moulin-Fournier said.

(Reporting by John Irish; Writing by Tim Cocks; Editing by Michael Roddy)