Ahmed Wali Karzai, a powerful figure in the southern province, was shot and killed by his guard on Tuesday and his burial Wednesday was attended by President Karzai.
Provincial authorities said the suicide bomber attacked as a number of high-ranking officials were at the memorial service, and the incident raised concerns about a power struggle in Kandahar province, the Los Angeles Times reported.
Those killed included a prominent cleric and a child. Another 15 people were injured, the Interior Ministry said.
The report said President Karzai was not at the service as he had returned to Kabul.
No one claimed responsibility for the attack, the Times said, but the Taliban had claimed that the guard who shot Karzai in his home had acted on its behalf. The man was shot and killed by other security personnel.
President Karzai has named Shah Ali Karzai, the full brother of the slain leader, as his successor.
Many observers told the Times Shah Wali can take over duties as head of his family, but wondered if he can be as influential as his slain brother in matters relating to tribal connections.