This article is by Taimoor Sha h, Alissa J. Rubin and Jack Healy.

KANDAHAR, Afghanistan — A suicide bomber detonated explosives hidden under his turban on Thursday after entering a mosque here where hundreds of people had gathered to pay respects to President Hamid Karzai’s half brother, who was assassinated on Tuesday.

The mosque attack killed at least three people besides the bomber and raised fears that Kandahar was entering a cycle of violence in the wake of the death of Mr. Karzai’s brother, Ahmed Wali Karzai, who was the most powerful man in the region.

The assassination and the mosque bombing, coming so close together, further unsettled people and increased their sense of vulnerability to attacks by the Taliban and other groups who might want to take advantage of the perceived lack of local leadership after Ahmed Wali Karzai’s death.

Little new emerged on Thursday about his killer, Sardar Muhammad, other than that he had run four security posts near the Karzai family’s ancestral village of Karz in the Dand district. Eleven men worked for him, and they were at Ahmed Wali Karzai’s house at the time of the killing, said the Kandahar police chief, Gen. Abdul Raziq. All of them have been detained, he said.