The Mauritanian army has launched an attack on an al-Qaeda training camp in neighbouring Mali and "completely destroyed" it, a Mauritanian security source said.
Friday's assault in the forest region of Wagadou in western Mali involved air strikes, the unnamed source told the AFP news agency, adding that the "terrorists" struck back with "heavy arms".
"The definitive toll on the enemy side will only be known at dawn but it will be heavy. The tents of the camp and three vehicles have been destroyed," the source said.
"Strong explosions were heard across a 20km radius, probably heavy weapons stocked in the camp," the source continued. "We are in control of the situation and the zone has been secured."
The attack was confirmed by a Malian soldier, Ousmane Diarra, who said the fighting was "very fierce".
Several military officials had earlier said al-Qaeda was trying to set up a new base in the Wagadou region.
Earlier this month, Mali and Mauritania agreed to lead a joint military operation to crush Al-Qaeda in the Islamic Maghreb, AQIM, the group's north African offshoot.
Mali and Mauritania have previously expressed concerns about the activities of the group, along with Nigeria and Algeria.
AQIM, which has its roots in Algeria, has bases in Mali, from where it carries out armed attacks and kidnappings, particularly of Westerners, and is a party to arms and drugs trafficking.