US Defense Secretary Chuck Hagel in an unannounced visit arrived Sunday in Afghanistan, hours after the Taliban released US soldier Bowe Bergdahl from five years of captivity, dpa cited reports as saying. Neither Afghan officials nor the US embassy in Kabul would confirm Hagel's visit, which he is reportedly using to talk to US commanders about the progress of Afghan security forces taking over security. The US ends its combat mission in Afghanistan by December, leaving 9,800 troops in the country until the end of 2016 if the new government signs the long-delayed security pact with Washington.