President Hamid Karzai has accused the United States of colluding with the Taliban to justify its presence in Afghanistan, dumbfounding US officials during a problematic visit by the new Pentagon chief. A joint news conference by Karzai and US Defense Secretary Chuck Hagel was cancelled Sunday, as the Afghan leader's allegations compounded the troubled nature of the visit after a security scare from twin bomb attacks on Saturday, AFP reported. "The bombs that were detonated in Kabul and Khost were not a show of force, they were serving America," Karzai said in a televised speech.