"I confirm that Ahmad Wali was killed inside his house," said Zalmay Ayoubi, spokesman for the governor of Kandahar province, where Ahmad Wali Karzai lived and was head of the provincial council.

Abdul Ghafar Sayedzada, head of the counter-terrorism department at the Interior Ministry said that the killing was probably the work of someone from Ahmad Wali Karzai's inner circle.

"It appears Ahmad Wali Karzai has been killed by one of his bodyguard, and there was nobody from outside involved," he said.

Ahmad Wali had survived at least one other assassination attempt in recent years.

A half brother of the president, Ahmad Wali was a critical power-broker who helped shore up his brother's influence in volatile southern Afghanistan.

He had also been accused of corruption and ties to Afghanistan's huge opium trade that helps fund the Taliban-led insurgency. Ahmad Wali Karzai had denied the accusations.

The United Nations said in a recent quarterly report that over half of all assassinations across Afghanistan since March were in Kandahar.