* Mali-Mauritania border zone secure after bloody offensive
* Al Qaeda operatives believed to have retreated
* Camps dislodged, weapons stockpiles found
By Tiemoko Diallo
BAMAKO, Aug 5 (Reuters) - Al Qaeda fighters have fled western Mali following a bloody military offensive to dislodge them from the area, Malian security sources said on Friday.
A joint force involving around a thousand Malian and Mauritanian soldiers began a sweep through the border region in late June after reports that al Qaeda's North African wing, Al Qaeda in the Islamic Maghreb, was setting up new bases.
"The camps have been dislodged, including one that was heavily equipped, and the weapons stockpiles were dismantled," a military official told Reuters, asking not to be named.
At least 27 people were killed in the joint offensive, including two Mauritanian soldiers, according to security sources, though AQIM claimed it killed 20 Mauritanian soldiers in a single clash in late June.
Al Qaeda's threat in the Sahel region has been on the rise in recent years, with the group receiving millions of dollars in ransoms from a string of kidnappings.
Security analysts believe AQIM has been able to get weapons and explosives from Libya since the rebellion there, and may be planning a high profile attack.
Another Malian security source said Al Qaeda's fighters fled the offensive in western Mali to the country's northeast, near the remote and lawless border region with Algeria and Niger.
"Last week armed men in about two dozen 4x4s were observed around Tarkint and Lere (near Timbuktu), and we feel that was the retreat," he said, also asking not to be named.
The threat of attacks by AQIM has hindered uranium mining operations in Niger and hit tourism there as well as in Mali, where the sector makes up as much as 18 percent of GDP.
AQIM came out of Algeria's radical Salafist movement but has moved south into the vast and lawless Sahel under pressure from Algeria's military. (Writing by Richard Valdmanis; Editing by Giles Elgood)