France is working with Nigerian and Cameroonian authorities to try and locate a French family being held hostage in Nigeria, President Francois Hollande has said, adding that it seemed they were being held in separate groups.

"The best thing for the moment is to work discreetly to first of all identify the exact place where our nationals are
being held, most likely in two groups, and work out how we can free them under the best conditions," Hollande said on Thursday.

A Nigerian security official said searches were ongoing near the porous border with Cameroon in the country's northeast, a region on the edge of the Sahara where insurgents and criminal gangs have long operated.

The members of the family, a couple, their children aged five, eight, 10 and 12 and an uncle, were abducted while holidaying in the West African nation of Cameroon on Tuesday by six armed suspected Islamists on three motorbikes.

Cameroon officials said they were taken across the border into Nigeria, though Nigerian military spokesmen have so far only officially said they have been unable to confirm that information.

Hopes for the family had been raised when a Cameroonian military source said earlier on Thursday they had been found safe and well in Nigeria.

The source said they were found abandoned in a house in Dikwa, about 100km from the border with Cameroon.

Kader Arif, France's veteran affairs minister, then confirmed that claim but later said he had merely passed on a media report. Issa Tchiroma Bakary, Cameroon's communications minister, bluntly stated that it was "a wild rumour".

'Cautious' operation

A Nigerian security official said "intelligence reports have shown that the abductors may be holding their victims ... around the Dikwa area," referring to a Nigerian town in the northeast.

"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."

It is the first time Western tourists have been kidnapped in Cameroon, although hostage taking frequently occurs off the Cameroonian coast, the last incident dating back to February 8.

Ansaru, a little-known Nigerian armed group, has claimed responsibility for the kidnapping of seven foreigners in a deadly weekend raid on a construction site in the country's north.

Foreign minister Laurent Fabius said France would not give in to "terrorists", an apparent warning that a ransom would not be considered.

The defense ministry said a team of French gendarmes arrived in Cameroon on Tuesday to help with the probe, adding that they were being "protected by French soldiers".

Source: Agencies