Nigerian security forces searched the country's northeast along the border with Cameroon on Thursday in a bid to free a French family kidnapped earlier this week, officials said.
"Intelligence reports have shown that the abductors may be holding their victims ... around the Dikwa area," a security official in the region said on condition of anonymity.
"But I must tell you we haven't got the exact location. Our men and other sister security agencies, especially our colleagues in the immigration service, are already on operation and we have the strictest instruction to carry out the operation with caution."
The family -- a couple, their children aged five, eight, 10 and 12 and an uncle -- was snatched in Cameroon on Tuesday by six armed suspected Islamists on three motorbikes.
Cameroon officials said they were taken across the border into Nigeria.