Al-Shabaab lost some of its territorial claims in recent fighting with pro-government and African Union forces.
The terrorist group, affiliated with al-Qaida, controls parts of a country where the central government struggles to exert authority.
Mohamed Abdi Kaliil, governor of the administrative district of Gedo in southwestern Somalia, told the United Nations' humanitarian news agency IRIN that thousands of people in the region were cut off from the capital by recent fighting.
"In the last couple of weeks, we have had some 5,000 people displaced by the conflict," he said. "Their main aim is to hide from the violence."
A local journalist who spoke to the news service on condition of anonymity said many area residents feared al-Shabaab was still "close by."
"This has created a great deal of apprehension and uncertainty as to what will happen next," the journalist said.
A mandate for the interim government in Somalia expires in August. The country had received praise from the international community for modest political gains.
There hasn't been a functioning central government in Somalia since the 1990s.