Grief-stricken Afghan President Hamid Karzai led thousands of mourners Wednesday at the funeral of his half-brother, a regional power broker who was assassinated a day earlier.

President Karzai wept openly, and at one point, climbed into the grave to kiss the face of the slain Ahmad Wali Karzai during the burial in the family village of Karz. The funeral took place among tight security in the southern province of Kandahar.

Ahmad Wali Karzai — chief of the Kandahar provincial council and a powerful figure in the country's south — was shot dead on Tuesday at his home in Kandahar city by a trusted longtime member of his own security team. The man, identified as Sardar Mohammad, was then killed by other guards.

The Taliban claimed responsibility for the assassination. But Afghan officials said it is not clear whether Wali Karzai's killing was related to the insurgency or to an internal feud.

Despite the Taliban's claim, President Karzai renewed his call to the Taliban to make peace following Wednesday's funeral. The Afghan leader has been pushing for insurgents to take part in the reconciliation process.

In Washington, the White House said President Barack Obama called Mr. Karzai early Wednesday to express condolences for the murder of the Afghan president's brother.

Kandahar is the birthplace of the Taliban and violence has increased as international troops work to clear the south of insurgents.

On Wednesday, the governor of nearby Helmand province escaped injury after his convoy was hit by a roadside bomb while traveling to the funeral. Two security officials accompanying Governor Gulab Mangal were wounded in the attack.

Immediately after Wednesday's burial, Mr. Karzai placed a turban on the head of another of his half-brothers, Shah Wali Khan, appointing him leader of the Popalzai tribe to which the Karzai family belongs.

Ahmad Wali Karzai was considered the most influential official in southern Afghanistan. Analysts say his death creates a power vacuum in the volatile region, where President Karzai relied on his brother to help maintain support among his ethnic Pashtun community.

While Wali Karzai was seen as a key power broker and an ally of the international forces fighting the Taliban, he was also accused of corruption, drug trafficking, and being on the CIA's payroll — allegations he denied.