The al-Shabab group claimed responsibility for the suicide attack in a statement on its Arabic media unit Shahada News Agency, the SITE Intelligence Group reported on Friday.
It put the number of dead at 11 and wounded at 18; its numbers on casualties in attacks often differ from government figures.
The Friday afternoon blast occurred at a checkpoint on a road leading to the parliament and the president's office and the shop is frequented by soldiers, the witness said.
The witness and medical personnel who were at the scene put the number of dead at seven and the wounded at up to eight.
Sadik Ali, a police representative, said the blast killed five people and wounded six others, adding the bomber was a member of al-Shabab.
"He killed five people... who were all drinking tea. The suicide bomber was one of the Kharijite terrorists," Ali said in a statement, using the term the government uses to refer to al-Shabab militants.
"I have counted and helped transport seven dead people and six others wounded, most of them soldiers," Ahmed Ali, a witness at the scene of the explosion, told Reuters.
In June, al-Shabab, which aims to topple the central government and impose its own strict interpretation of Islamic law, killed 54 Ugandan soldiers at their base southwest of Mogadishu.
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