(CNN) -- Islamist rebels in Nigeria on Monday released video of a French family kidnapped in neighboring Cameroon last week, leading France to blast the scene as one of "cruelty without limits."
The seven-member family was flanked by armed fighters from the Boko Haram movement in the brief video. One of the captive men reads a statement demanding that Nigeria and Cameroon free jailed members of Boko Haram, which is battling to establish Islamic rule in northern Nigeria, and their families.
"Meet all the demands we have mentioned, and if you leave out one of them, we will kill these hostages," the masked man says.
The family -- a couple, their four children and an uncle -- were seized in a national park in remote northern Cameroon on February 19. Authorities in Cameroon said they were quickly spirited across the border into Nigeria.
French Foreign Minister Laurent Fabius denounced the video, saying, "All of the state services are mobilized to free our countrymen."
"For all of us, these images are terribly shocking. They demonstrate cruelty without limits," Fabius said in a statement released Monday afternoon.
The kidnapping has raised fears of Westerners being targeted by Islamist militant groups in Africa in the wake of the French military intervention against other Islamist rebels in Mali. The masked man in the video says French President Francois Hollande "started war against Islam, and we must fight him everywhere."
"He also should learn that we have spread everywhere to save our oppressed brothers," the masked man adds.
The father works for the French company GDF Suez and is based in Yaounde, the capital in southern Cameroon. GDF Suez, which is developing a natural gas liquefaction project in Cameroon, said it was working closely with the French Foreign Ministry.