The attack took place in western Mali’s Wagadou forest in a border zone where AQIM fighters are known to operate.
Governments in Africa’s Sahel region are on heightened alert since the killing of al Qaeda leader Osama bin Laden in Pakistan in May.
The source declined to give further details about the attack, saying the government was preparing a statement.
A report from French news agency AFP, quoting Mauritanian security sources, said Mauritanian forces destroyed the camp, causing heavy casualties to the AQIM members and injuring four soldiers.
Mauritanian officials contacted by Reuters did not comment.
AQIM has its roots in Algeria’s Salafist movement, but has pushed south into the lawless Sahel region in recent years where it funds operations by collecting kidnap ransoms and by siphoning off the West African drugs trade.
Security analysts have said AQIM may be planning retribution attacks since U.S. forces killed bin Laden, and also may have new access to weapons and explosives from Libya since an uprising there shook the