Mauritania troops killed at least 12 militants of al-Qaida's north African wing during an offensive along the border with Mali Saturday.
The French news agency, AFP, quotes a Mauritania official as saying two of the country's troops were killed and four wounded.
It is not clear if the deadly assaults are linked to the kidnapping of five French nationals and two Africans in Niger.
French officials believe al-Qaida's North African branch carried out the abductions early Thursday, although no one has claimed responsibility.
Security officials say the seven hostages kidnapped in the northern Niger town of Arlit were spotted Friday crossing the border into Mali with their kidnappers.
The kidnapping victims include a man who worked for the French nuclear company Areva and his wife, as well as five of the company's subcontractors.
Authorities have urged all French citizens working in the area to evacuate the mining town.
In 2008, four French nationals working for Areva were held for several days by a local rebel group, the Niger Justice Movement.
Al-Qaida in the Islamic Maghreb kidnapped a 78-year-old Frenchman in Niger in April and later killed him.
France says they are at war with the group.
Some information for this report was provided by AFP and AP.