US Defense Secretary Jim Mattis arrived in Afghanistan today as President Donald Trump's administration looks to construct its strategy for the war-torn country, where resurgent Taliban militants continue to make gains. <br/><br/>Mattis is expected to meet Afghan officials and US troops while in Kabul, but his arrival coincided with an announcement that his Afghan counterpart, Defence Minister Abdullah Habibi, and the Afghan army chief of staff had resigned after more than 140 Afghan soldiers were killed in a Taliban attack last week.