Ahmed Wali Karzai, the powerful half-brother of Afghanistan President Hamid Karzai, has been killed by one of his security guards inside his house in Kandahar, raising the prospect of turmoil in a city widely seen as the key to the war in Afghanistan.

The president confirmed the death at a press conference in Kabul intended to mark the visit of the French president, Nicolas Sarkozy, to the capital.

"Ahmed Wali Karzai was killed at about 11.30am," General Abdul Razaq, Kandahar's chief of border police, said. "He was killed by his bodyguard inside his house." Officials said the assassin, named as Sardar Mohammed, reportedly Ahmed Wali Karzai's chief of security, had been killed on the spot.

"After Sardar Mohammed killed Ahmed Wali Karzai, other bodyguards shot Sardar Mohammed," Colonel Mohammad Mohsen, of the Afghan national army 205 Atal (Hero) Corps in Kandahar, said.

"The bodies have been taken to the [local] hospital. We expect some officials including President Karzai to come to Kandahar for his brother's funeral."