"We have strategically abandoned our positions in the towns of Ansogo and Bourem to reinforce our positions in Gao," the army said in a statement.
Gao is the largest town in northern Mali that remains under the control of Mali's new ruling junta.
It is also a regional military base and believed to be one of the rebel's next targets along with the fabled city of Timbuktu.
The MNLA (Azawad National Liberation Movement) in mid-January relaunched a decades-old fight for the independence of what the Tuareg consider their homeland in the vast desert north.
After heavy fighting, Tuareg separatist rebels and an allied armed Islamist group on Friday entered the strategic town of Kidal, 1,000 kilometres (620 miles) from the capital, on Friday.
On its website, the MNLA spokesman Bakaye Ag Hamed Ahamed said it would "continue the offensive against two other regional capitals to dislodge the Malian regime and its army."