Some people were watching the European soccer final between Spain and England on a screen inside the café on Sunday when a car loaded with explosives blew up outside, said Maj. Abdifitah Aden Hassa, spokesman for Somali police. He told reporters that at least 20 other people were injured in the attack.
Pictures posted online and purporting to be from the scene showed a fire burning outside the café in the aftermath of the explosion.
"Some of the spectators got injured while trying to jump the perimeter wall of the café, and others got wounded in a stampede," witness Ismail Adan said.
Most of the victims were in the street at the time of the explosion, he said.
It was not immediately clear who was responsible for the attack.
Attacks by the Islamic militant group al-Shabab are frequently reported in Mogadishu and elsewhere in Somalia. The group opposes Somalia's federal government, which depends on the support of foreign troops to stay in power.
But Mogadishu had been mostly peaceful in recent months.
That calm was broken on Saturday with an attempted jailbreak by inmates inside a Mogadishu prison. In that attack, in which at least eight people were killed, prisoners convicted for their roles in al-Shabab attacks exchanged fire with prison guards before they were killed.
Somalia's government is conducting a high-profile offensive against the extremist group, which the US has described as one of al-Qaeda's deadliest organisations.
Somali President Hassan Sheikh Mohamud has declared "total war" against the extremists, who control large parts of central and southern Somalia and have been the target of scores of US airstrikes in recent years.
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