Somalia’s army, with the backing of an AU force and increased US support, is trying to quash al-Shabaab, an al-Qaeda-linked Islamist militant group that has waged a decade-long war to impose its version of Islamic law in Somalia.

While the group was driven out of Mogadishu in 2011, it still stages regular gun and bomb attacks.

"The barbaric attack points to a trend in which areas known for vibrant activity and thriving businesses are targeted," the AU Mission in Somalia said in an e-mailed statement.

"The cowardly act attests to the deliberate effort by al-Shabaab to deter progress being made by hardworking Somalis to stabilise their country."

The AU appealed to the international community for "more co-ordinated and robust international support" to Somalia’s institutions in their fight against extremist groups.

"It is now clear that without adequate and appropriate support to Somalia, many of the security gains made in recent years could be reversed," it said in a statement.

The Turkish government sent doctors while neighbouring nations including Djibouti, Kenya and Ethiopia agreed to provide medical supplies, according to the Information Ministry statement.

President Mohamed Abdullahi Farmajo declared three days of mourning and ordered flags flown at half-staff after the bombing.