The Islamic State affiliate in Afghanistan has ramped up its recruitment efforts in the past year, American officials and analysts say, rolling out a sophisticated propaganda campaign designed to persuade disaffected Muslims to carry out terror plots in the U.S. and other Western countries. 

The recent arrest of an Afghan accused of plotting an Election Day attack in the U.S., as well as recent plots in France, Sweden and elsewhere, highlight the growing threat posed by ISIS-K, officials and…