Al Shabaab, which is carrying out increasingly deadly bombings despite losing most of its territory to African Union peacekeepers supporting the Somali government, was behind the attack, Abdiasis Abu Musab, the Islamist militant group's spokesman for military operations said.
Somalia's President Mohammed Abdullahi Mohammed speaks at his inauguration ceremony in Mogadishu, Somalia in February.
Somalia's President Mohamed Abdullahi Mohamed last Thursday pledged a new war against Shabab, giving militants 60 days to surrender or "face the consequences". Targets have included hotels, military checkpoints and the presidential palace.
The Mogadishu attack against the army convoy was claimed by the Shabab extremist group and came only days after Mohamed Jama Irfid, who was not hurt, was appointed to head the country's army, a security source said. A widespread drought has brought the country to the brink of starvation and the United Nations says half the population will need aid by July.
Mohamed did not mention the new USA directive, but emphasized that Somali troops should take the lead and added in a statement: "We want to pardon the Somali youth who were misled by al Shabaab".
"The government cordially welcomes them". We do not want to kill our youth. "I saw five soldiers being carried onto a pickup truck", some of whom were dead, said eyewitness Abdukadir Moalim.
Somalia's new military chief survived a suicide vehicle bomb attack Sunday just moments after he was sworn in with a mandate to launch a new offensive against Islamic extremists.
The fragile central government continues to have worldwide backing as well as the 22,000-strong AU force.