"Civilians fled to bush areas, some were barefoot with no belongings."
Al-Shabab has been fighting to topple Somalia's African Union-backed government, which is led by Sharif Ahmed, the president.
Al-Shabab controls most of southern and central Somalia, but it has failed to reach the well- protected presidential compound and topple Ahmed.
"Large forces of al-Shabab ... attacked us but we chased them away after fierce fighting," Abdullahi Sheikh Abu Yusuf, an Ahlu Sunna Waljamaca spokesman, said.
"Their goal was to capture Dhusamareb, but they failed."
A local al-Shabab official said that his forces would seize the whole region from the pro- government militia.
"We shall never stop fighting until our fighters capture the whole region and impose the Islamic sharia," Yusuf Sheikh Isse, a senior al-Shabab official, told reporters.
Somalia has had no effective government for 19 years and Western nations and neighbours say the country is used as a shelter by fighters planning attacks in East Africa and further afield.
More than 21,000 civilians have been killed since the start of the violence.