Security is tight in Afghanistan's southern province of Kandahar as thousands of mourners gather for the funeral of President Hamid Karzai's half brother, who was assassinated on Tuesday.

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

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.

The commander of U.S. and NATO forces in Afghanistan, General David Petraeus, condemned Wali Karzai's murder and said NATO forces will support the Afghan government's efforts to bring those responsible to justice.

The Obama administration also condemned Wali Karzai's death “in the strongest possible terms.” White House spokesman Jay Carney said Tuesday the U.S. will work with Afghan authorities as they investigate the killing.

Meanwhile, Italian defense officials said on Tuesday that a roadside bomb killed an Italian soldier in western Farah province. Early Wednesday local time, NATO said two of its service members were killed in separate attacks in the south. A NATO statement said one soldier died in a bomb blast, while the other was killed in an insurgent attack.

In other violence, Afghanistan's spy agency said it foiled an attempt by a group of eight terrorists to kill Interior Minister Bismillah Mohammadi during his visit to eastern Paktia province.

A spokesman for the National Directorate of Security, Lutfullah Mashal, said three policemen and five insurgents were detained last week ahead of Mohammadi's visit. He said the policemen were stationed at Paktia's police headquarters and were in contact with a member of the Haqqani network based in Pakistan's tribal belt. Afghan officials said the terrorists had provided the police officers with explosives, suicide vests and weapons.