The car following the Somali leader’s car exploded, leaving four of the fatalities burnt beyond recognition.
One government source said
unidentified attackers had thrown a handgrenade under Gedi’s car as it passed seconds before the landmine blast in an apparent co ordinated attack.
One of the 20 passengers wounded in the attack said car tyres were also shredded by bullets.
"Five seconds after the blast, there was an exchange of fire, I don't know who between," the man said from his hospital bed.
The attack has raised tensions in the capital Mogadishu, a lawless city largely controlled by political foes of the PM.
Gedi was due to hold talks with a dissident faction of ministers based in Mogadishu to end a government rift that has stirred fears of renewed civil war.
He visiting for only the second time since he was appointed as part of a Transitional Federal Government formed at peace talks in Kenya during 2004.
14 people were killed in an explosion on Gedi’s first visit to Mogadishu at a rally he was addressing in May.
Gedi went on radio after today's blast to say he would meet other ministers in Mogadishu. He did not mention the blast.