BAUCHI, Nigeria — A little-known Islamic extremist group claimed responsibility Monday for the kidnapping of seven foreign workers from northern Nigeria, threatening their safety if anyone tried to intervene.

The group that calls itself Ansaru issued a short statement, in which it said its fighters kidnapped the foreigners Saturday night from a construction company’s camp at Jama’are, a town about 125 miles north of Bauchi, the capital of Bauchi state.