Iftin Hassan Basto, a tribal leader who has fought with the Islamist group in the past, said six people, including a child, were killed and seven injured.
"The explosion occurred soon after I entered the house," Basto said in a statement.
"My security guards saw a man who tried to infiltrate them and when they confronted him, he blew himself up."
The alleged attack took place in the port city of Kismayo, a former stronghold of Somalia's Shebab militants.
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"There was no attack on his home, but his amateur guards fired a rocket launcher inside the house," Abdulaziz Abu Musab, Shebab's military spokesman told AFP.
"The Shebab fighters have conducted no assault (...) the damage was self-inflicted by his soldiers," he added.
One witness to the explosion, Ali Mohamed, said: "The explosion was huge and several dead bodies were removed from the house. Security forces have cordoned off the area after the explosion."
Kismayo was a former stronghold of the Shebab before Kenyan troops -- along with local warlord Ahmed Madobe -- captured it in late September 2012.
Major fighting occurred between the two groups in Kismayo, but Basto has since joined sides with Madobe.
Basto claimed to have fought with Shebab militants outside Kismayo in the past, and said he had been threatened by the group.
"We knew they were planning such attacks and we will continue fighting these terrorists," he said.