KABUL, Afghanistan — At least five people were killed and 15 injured on Thursday when a suicide bomb exploded at a Kandahar mosque where hundreds were paying their respects to Afghan President Hamid Karzai's powerful half-brother, who was slain this week.

The bombing at the Red Mosque, combined with an explosion a few minutes later at a police station in Kandahar that killed an officer, raised concerns that the volatile southern city was falling into a violent spiral following the killing Tuesday of Ahmed Wali Karzai, long the region's undisputed kingpin.

The mourners at the mosque, one of the city's largest, included several top Afghan officials. Among those killed were the chief of the province's clerical council, Hekmatullah Hekmat, and a young boy, according to the provincial governor, Tooryalai Wesa.

No group immediately claimed responsibility for the attack, which officials and an eyewitness said occurred when a suicide bomber detonated explosives hidden in his turban. Witnesses also said that security forces weren't carefully searching the mourners before the attack.

"It was an un-Islamic act," Wesa said at a press conference.

Ahmed Wali Karzai, the head of the Kandahar provincial council, was killed Tuesday in an argument with a family associate, sending shock waves through the Afghan government. The slain Karzai was President Karzai's most important representative in the insurgent-plagued southern region, a hotbed of both the Taliban and the drug trade, and experts believe that his death could set off a wave of violence as insurgents and rival groups jockey to fill the power vacuum.

The slain Karzai was laid to rest Wednesday in an emotional burial service at his family's ancestral cemetery north of Kandahar, in the village of Karz.

Zohori is a McClatchy special correspondent.