Gunmen from Nigeria kidnapped a French family that included four children on Tuesday in northern Cameroon near the border with Nigeria, French President Francois Hollande said.
They were apparently tourists, he said.
The risk of attacks on French nationals and interests in Africa has risen since France sent forces into Mali last month to help oust Islamist rebels occupying the country's north.
"They have been taken by a terrorist group that we know and that is in Nigeria," Hollande told reporters during a visit to Greece. Islamist militants in northern Nigeria now pose the biggest threat to stability in Africa's top oil-producing state.
Radio France International had earlier reported the kidnapping, saying that the seven people were nabbed by armed men on motorbikes and were being taken towards Nigeria.
Western governments have grown concerned that Nigeria's radical Islamists may link up with groups elsewhere in the region, particularly al-Qaida's North African wing, Al-Qaida in the Islamic Maghreb, given the conflict in nearby Mali.
The seven tourists were abducted at around 7 a.m. in a village about six miles from the Nigerian border near the Waza national park and Lake Chad in the extreme north of Cameroon where Westerners often go for holidays.
It was the first case of foreigners being seized in the mostly Muslim north of Cameroon, a former French colony.
"I see the hand of (Nigerian militants) Boko Haram in that part of Cameroon. France is in Mali, and it will continue until its mission is completed," Hollande said.
France intervened in Mali last month when Islamist rebels, after hijacking a rebellion by ethnic Tuareg MNLA separatists to seize control of the north in the confusion following a military coup, pushed south towards the capital, Bamako.
Eight French citizens are already being held in West Africa's Sahel region by al-Qaida-affiliated groups.
Cameroon Information Minister Issa Tchiroma Bakary said he could not immediately confirm the kidnapping report.
On Sunday, seven foreigners were snatched from the compound of Lebanese construction company Setraco in northern Nigeria's Bauchi state, and al-Qaida-linked Ansaru took responsibility.
Northern Nigeria is increasingly afflicted by attacks and kidnappings by Islamist militants. Ansaru, which rose to prominence only in recent months, has also claimed the abduction in December of a French national who is still missing.
An Ansaru statement said kidnappings were driven by "the transgression and atrocities done to the religion of Allah by the European countries in many places, such as Afghanistan and Mali."