The blast, which comes amid a wave of attacks in the capital by Al-Qaeda-linked Shebab rebels, targeted a bar near the City Palace hotel close to Somalia's intelligence and security headquarters.
The hotel is known to be popular with officials from the country's internationally-backed government, and witnesses said the target may have been a senior security official who was in the area at the time.
Initial reports from police said a soldier was killed and several others hurt in the blast, which appeared to be from a car bomb.
That attack, the latest in a string of Shebab raids against high-profile targets in Mogadishu, prompted the resignation of Somalia's minister of national security.
Recent Shebab attacks have targeted key areas of government or the security forces, in an apparent bid to discredit claims by the authorities that they are winning the war against the Islamist fighters.
African Union and Somali government troops launched a fresh offensive in March against Shebab bases, and although they seized a series of towns, the insurgents are thought to have fled in advance and suffered few casualties.