US ambassador Ryan Crocker said the US strongly condemned the killing of Ghulam Haidar Hamidi by a suicide bomber in Kandahar, Afghanistan.
Mr Hamidi's death comes two weeks after the assassination of the brother of Afghan President Hamid Karzai in the same city.
Mr Crocker said the attack was "indication again of both the challenges that Afghanistan faces, but also the extraordinary resilience of the Afghan government and people."
Afghan forces are due to take over full security control by 2014 as foreign troops withdraw. This has given rise to fears this will lead to a resurgence in violence by the Taliban, a prospect the ambassador rejects.
"I would judge that the Taliban is now damaged to the point where they can no longer conduct field operations and they have had to regroup and figure out what they can do and in some cases that has been assassinations,” he said.