Kabul, Afghanistan (CNN) -- The half brother of Afghan President Hamid Karzai was shot dead at his home in Kandahar on Tuesday, authorities said.

Ahmed Wali Karzai, the Kandahar provincial council chief, was killed during a gathering, said Tooryalai Wesa, provincial governor. He did not know a motive.

While the governor initially said a friend killed Karzai, his spokesman later clarified that the death was at the hands of a guard.

Saidkhan Khakrezwal, a member of the Kandahar provincial council, told CNN he and others were with Ahmed Wali Karzai when a guard named Sardar Mohammad came into the room and asked to talk to him.

The guard then "takes Wali to another room and shoots him with a pistol that he had in his hand," Khakrezwal said. The shooter was shot dead by other guards.

Sardar Mohammad was a trusted man who had worked as a guard for Karzai for eight years, Khakrezwal said. He was also a commander for a police post where there were about 30 policemen.

The Taliban claimed responsibility for the shooting, saying that the guard accused of shooting him was working for them.

Karzai suffered bullet wounds to his head and chest, said Mohammad Dawood Farhad, the head of Kandahar Hospital.

"My brother Ahmad Wali Karzai was killed today," said the Afghan president in a previously scheduled news conference with visiting French President Nicolas Sarkozy.

"The Afghanistan people have suffered a lot. Every Afghan family has suffered. I hope one day these sufferings end."

White House Press Secretary Jay Carney said President Barack Obama comdemned Karzai's murder and extended thoughts and prayers to his family.

"The United States condemns in the strongest possible terms the murder of President Karzai's half brother in Kandahar," Carney said. "There's been some claims and we will certainly work with the Afghan authorities on that, but right now the moment here is a personal one and we express our condolences."

Gen. David Petraeus, the commander of U.S. and NATO forces in Afghanistan said ISAF will help the Afghan government "bring justice" to those involved in the killing.

"President Karzai is working to create a stronger, more secure Afghanistan, and for such a tragic event to happen to someone within his own family is unfathomable," Petraeus said.

Ahmed Wali Karzai, who has been dogged by drug dealing and corruption accusations, had been the subject of WikiLeaks cables leaked last year.

Without being prompted, he discussed the accusations with a senior U.S. diplomat, according to one of the cables. He said that the claims are part of a campaign to discredit him and offered suggestions on how to stop drug dealing.

"He is willing to take a polygraph anytime, anywhere to prove his innocence," the cable said.

"He suggested that the coalition pay mullahs to preach against heroin, which would reduce demand for poppy cultivation."

A U.S. official who authored another cable wrote that even though he must be engaged as head of Kandahar's provincial council, "he is widely understood to be corrupt and a narcotics trafficker."

He said Karzai's "reputation for shady dealings" should be considered when he recommends "costly infrastructure projects.

The official said dealing with people like Ahmed Wali Karzai represents a major challenge in Afghanistan: Fighting corruption and building support for government when government officials are corrupt themselves.

Karzai "appears not to understand the level of our knowledge of his activities, and that the coalition views many of his activities as malign, particularly relating to his influence over the police," the author of the first cable said.

In addition to discussions of war, drugs and Afghan politics, a comment in one of the cables also addressed his days as a restaurant owner close to Chicago's Wrigley Field, the iconic baseball stadium.

"His restaurant was a hub for American(s) in the Midwest who had worked or lived in Afghanistan prior to the Soviet invasion," the cable read.

CNN's Matiullah Mati contributed to this report.