Afghan defense chief quits over attack; U.S. warns of 'another tough year'

By Idrees Ali and Josh SmithKABUL (Reuters) - Afghanistan's defense minister and army chief of staff resigned on Monday after the deadliest Taliban attack on a military base, and U.S. Defense Secretary Jim Mattis said he was "under no illusions" about the problems facing the country.Mattis, visiting as the United States looks to craft a new Afghanistan strategy, held talks with Afghan President Ashraf Ghani, officials and U.S. commanders, who want more troops.