Burundi has sent an advance party of 100 soldiers to Somalia to join the African Union (AU) force charged with keeping peace there.
Violence continues almost daily to affect Mogadishu's population
The troops flew into Mogadishu's heavily guarded airport just hours after a clash between government forces and rebels left four people dead.
They will join 1,600 Ugandan soldiers in a force which is meant to reach an eventual strength of 8,000.
Countries have been slow to offer troops amid the continuing conflict.
An army spokesman in the Burundian capital, Bujumbura, Col Adolphe Manirakiza, said the troops had been sent to "prepare the ground" for a further 1,700 soldiers.
These would arrive over the next two weeks, he told Reuters news agency.
The African Union force is for now limited in what it can do
Uganda's soldiers have, in the absence of reinforcements, been restricted to guarding Mogadishu's sea and air ports and presidential palace, or providing security for top Somali government officials.
The latest fighting in Mogadishu flared up when Islamist militants attacked government troops and their Ethiopian allies, reportedly at a former factory they use as a base.
Ethiopian troops used tanks and artillery to repel the attack, residents told The Associated Press.
At least four Somali civilians were killed and eight injured as the Ethiopians reportedly responded to mortar and machine-gun attacks with tanks and artillery.