Suspected Islamist militants kidnapped seven French holidaymakers from one family, including four children, in Cameroon on Tuesday, business, diplomatic and security sources said.
GDF Suez confirmed that one of its employees had been kidnapped with his family.
French President Francois Hollande said during a visit to Athens that he was informed of the kidnapping by a Nigerian "terrorist group that we know well", without naming it.
"What is most probable is they will be taken to Nigeria," Hollande told reporters, adding that France was doing everything possible to prevent that outcome.
A statement from GDF Suez said the employee was based in the Cameroon capital Yaounde and that he and his family were vacationing in the north of the west African country.
The French energy company is developing a natural gas liquefaction project in cooperation with national oil and gas group SNH in southern Cameroon.
A Western diplomat in the region told AFP that six armed kidnappers on three motorbikes abducted a couple, their four children and an uncle in the northern village of Dabanga near the Nigerian border.
The children are aged five, eight, 10 and 12, the diplomat said.
A source close to the French embassy in Yaounde said the family had earlier visited Waza National Park in northern Cameroon.
Asked whether the kidnapping could be a reprisal for France's military offensive against Al-Qaeda-linked groups in northern Mali, Hollande spoke of Nigeria's Islamist Boko Haram group.
"I note in particular the presence of a terrorist group, namely Boko Haram, in that part of Cameroon, and that's worrying enough," he said.
A Cameroonian security source also told AFP: "We have strong suspicions regarding the Islamist sect Boko Haram," which is blamed for killing hundreds of people in an insurgency in northern Nigeria since 2009.
Some Boko Haram members are believed to have trained with militants of Al-Qaeda in the Islamic Maghreb (AQIM) in northern Mali.
Former French defence minister Hervin Morin said Tuesday it was "much too early to say" whether the kidnapping was linked to the Mali offensive but added that since the start of the conflict he had expected a test of French resilience.
"We're very likely seeing the first actual case because, even if it's a different terrorist movement, all these Islamist movements are connected by a common struggle, that of a fight against the West," he told television channel BFMTV.
An anonymous source at the Waza nature reserve said the holidaymakers had visited it on Monday. "They slept in the park's tourist camp (and) they left this morning," the source said.
A security source in the area told AFP that security forces were hunting for the kidnappers along the border with Nigeria.
Though it was the first abduction of Western tourists on Cameroonian soil, there have been several hostage-takings off the coast, a region believed to be rich in oil and gas.
Cameroonian authorities have attributed attacks and kidnappings off the Bakassi peninsula neighbouring Nigeria to pirates.
In December, French engineer Francis Collomp was kidnapped in Nigeria in an act claimed by the Nigerian radical Islamist group Ansaru, which is thought to be a Boko Haram splinter group.
On Monday, Ansaru also claimed the kidnapping of seven foreigners in a deadly weekend raid on a construction site in northern Nigeria.
Tuesday's abduction brings the total of French hostages abroad to 15, all in Africa and at least six of whom are being held by AQIM.
According to the US monitoring group IntelCenter, France is the Western country with the highest number of hostages taken, followed by the United States with nine.
Cameroon, a former French colony of 20 million people, has vast ethnic, linguistic and religious diversity and counts no fewer than 10 active rebellions.