Since the start of this year the group which is linked to al-Qaeda has retaken at least 10 towns from Ethiopian and African Union troops. They retook four town in the past month.
Analysts say that the change in fortune of al-Shabab is in part due to events outside Somalia. The anti-government protests in neighbouring Ethiopia is the reason, they argue.
Ethiopia has thousands of troops in the Horn of Africa country as part of an agreement with the Mogadishu government to fight the armed group.
But Addis Ababa denies the claim.