KABUL, Afghanistan (AP) — A high-level meeting to lay out security plans for Afghanistan's upcoming parliamentary elections had just concluded when an elite Afghan guard turned his gun Thursday on the departing delegation in an attack that killed the powerful Kandahar police chief but missed the top U.S. commander in the country, Gen. Scott Miller.

The audacious assassination strike, which killed at least one other senior Afghan official and was claimed by the Taliban, underscored the harrowing lack of security in Afghanistan just two days before national elections and more than 17 years after...