Four children are among those kidnapped.

(Reuters) – Gunmen claiming to be from Nigeria’s Boko Haram Islamist group threatened on Monday to kill a kidnapped French family of seven if authorities in Nigeria and Cameroon do not release Muslim militants held there.

French ministers said they believed the three adults and four children seized in Cameroon’s far north near the Nigerian border on Tuesday were being held by Boko Haram which has killed hundreds to try to carve out an Islamist state in Nigeria.

The first sign of the family since they were captured came in a video posted on YouTube in which they appeared surrounded by three gunmen wearing turbans and dressed in camouflage.

“We have been taken by Jama’atu Ahlis Sunna Lidda’awati wal-Jihad,” one of the male hostages said in the video, referring to the name in Arabic of Nigeria’s Boko Haram militants.

“They want the liberation of their brothers in Cameroon and their women imprisoned in Nigeria,” the man added, speaking in French as he sat on the floor beside another man, a veiled woman and four children.

“A video of the French family kidnapped in northern Cameroon last Tuesday has just been posted by Boko Haram,” said French Foreign Minister Laurent Fabius. “These images are terribly shocking and show a cruelty without limits.”