Clinton calls Karzai to condole brother's death

"The United States condemns this murder in the strongest terms. For too long, the people of Afghanistan have suffered under the threat of violence, intolerance, and extremism," Clinton said after the phone call.

"We join President Karzai in his prayer for peace and stability in Afghanistan and remain committed to supporting the government and people of Afghanistan in their struggle for peace," she said.

White House Press Secretary Jay Carney said the US condemns in strongest possible terms the murder of President Karzai's half-brother in Kandahar.

"We don't know who is responsible. There have been some claims and we will certainly work with the Afghan authorities on that, but right now I think the moment here is a personal one, and we express our condolences and condemn the murder," Carney said in response to a question at his daily news conference.