Nairobi - Somalia's Al-Qaeda linked insurgents, on the back foot after months of losses, are eyeing a potential withdrawal of arch-foe Ethiopia in the volatile southwest, raising security and humanitarian concerns.
Heavily armed Shabaab fighters swept into the town of Hudur, capital of Bakool region, just hours after Ethiopia's surprise withdrawal from the town on Sunday.
Hot on the heels of the Ethiopians - the strongest military power in the southwest region ever since their November 2011 invasion - fled allied Somali militia forces and a column of some 2 000 terrified civilians.
Security sources say the withdrawal from Hudur could signal a wider pull out of Ethiopian forces including from the key city of Baidoa, warning that if this happens, the 17 000-strong African Union mission (Amisom) would be hugely overstretched.
"Everything suggests Ethiopia is determined to withdraw from Baidoa" in coming days, a security source told AFP.
Ethiopia, which has repeatedly said it wishes to withdraw, is reportedly frustrated that its requests for Amisom troops to take over its positions have been ignored.
"The Ethiopians have been talking for quite a while of how much they want to leave...so far it was seen more as a posture," said a source close to Amisom, adding they were frustrated at how much the military operation was costing.
Whether Ethiopia continues to withdraw also depends on the reaction of the international community and whether the Shabaab reoccupy the areas they pull out from, the source added.
The withdrawal from Hudur "is a reminder that what they do is of strategic importance and that the Shabaab is not defeated," the source added.
Relations between Addis Ababa and the Somali government are also tense, with a parliamentary delegation travelling to Baidoa on Sunday in a bid to persuade Ethiopia not to leave, a humanitarian source there said.
Addis Ababa - long seen as a traditional enemy of Somalia - is a controversial presence in Somalia. Ethiopia entered Somalia in a 2006 US-backed invasion, but was driven out three years later by a bitter insurgency.
But while Shabaab forces are weak and unable to hold out against the heavy weaponry of Ethiopia or Amisom troops, Hudur's capture marked a sharp turnaround and a major boost to their morale.
Sources say that while their return to Hudur was expected, the speed with which they retook the town took many by surprise.
"If Al-Shabaab reoccupy all the places Ethiopia withdraws from, it would change things," the Amisom source said, adding that Hudur's rapid capture "clearly shows that holding ground is not enough to win over an insurgency."
Amisom would struggle at its current capacity to take over Ethiopian positions, while Somali troops who worked closely with Ethiopian troops would not necessarily cooperate so well with other forces, sources said.
Hudur's capture, the Shabaab's most important territorial victory for over a year, prompted jubilant celebrations amongst the Islamists, who vowed to "wage jihad" until total victory in messages posted on its Twitter account.
Top Shabaab military commander Mukhtar Robow led the celebrations in the town.
So far, Hudur is the only major town Ethiopians have pulled out of, but with troops packing kit in Baidoa in apparent preparation to leave, many are worried as to the impact of a retreat.
Security sources say several thousand Ethiopian troops have dominated southwestern Somalia since their 2011 assault on Shabaab bases in November 2011, shortly after Kenyan forces invaded Somalia from the far south.
Kenyan troops have since joined Amisom. Ethiopian forces have remained separate, although they collaborate with the mission.
While Amisom already have a significant force in Baidoa, reinforcements are battling to open up the final 50km stretch of road connecting the city with Mogadishu, some 250km to the southeast.
But given the large amount of Ethiopia's heavy equipment and weaponry based in Baidoa, troops would be unlikely to be able to stage a rapid pull-out as they did in Hudur.
"The behaviour of the Ethiopians is ambiguous," another security source said, asking whether they were "really leaving or pretending?"