At least 10 people were killed in an explosion when a suicide bomber drove his car into a tea shop near the national security headquarters in Somalia's capital, a senior police officer said to the Reuters news agency.
The al-Qaeda linked group, al-Shabab, said it carried out the attack on Thursday and threatened more.
"We are responsible for the car bomb blast," Sheikh Abdiasis Abu Musab, al Shabaab's military operations spokesman, told Reuters.
"We targeted the national security forces who were sitting in the tea shop. Today's blast was part of our operations in Mogadishu and we shall continue," he added.
The blast is the second in almost a week after al-Shabab said it was behind an attack on the president's palace on Friday.
"A bomber swerved his car bomb into a tea shop where national security men were sitting and blew up. So far we have confirmed 10 people dead including national security forces and civilians. The tea shop was completely destroyed," Colonel Abdikadir Hussein, a senior police officer, told Reuters.
Abdullahi Hassan, the district commissioner of Mogadishu's Abdiasis district, said the target of the attack was a national security car passing the tea shop.
A Reuters witness counted eight bodies.
Al-Shabab ruled most of the southern region of Somalia from 2006 until 2011 when African Union forces drove them out of Mogadishu and then expelled them from most urban centres.
The group, which wants to impose a strict version of Islamic law, still holds swathes of rural territory in southern Somalia and some smaller towns, including the major coastal stronghold of Barawe.