At least four soldiers were killed and several injured in a landmine explosion at Hawo Abdi, about 25 km south of Mogadishu, on Tuesday, authorities said.
The officers were killed when a landmine planted on the road hit a vehicle of a convoy heading to Afgoye district, Xinhua quoted a senior police official as saying.
Security officials arrested one of the suspects who was being interrogated over the incident, which has caused panic among the public, he said.
Al-Shabab claimed responsibility for the latest attack, saying its fighters had killed six government soldiers on board.
The Al-Qaeda linked group of Al-Shabaab has carried out two other deadly attacks in Mogadishu and Baidoa towns since Friday last week, killing more than 40 people.