US says Afghans must defend their country as Taliban takes more ground

Comments distancing the US from the conflict come as militants capture more cities and violence escalates

The US has said it is up to Afghan security forces to defend the country after Taliban militants captured a sixth provincial capital, along with border towns and trade routes.

Fighting in Afghanistan's long-running conflict has escalated dramatically since May, when the US-led military coalition began the final stage of a withdrawal set to be completed before the end of the month.